diff --git a/src/cli/mod.rs b/src/cli/mod.rs
index 7a8a915..6eb64aa 100644
--- a/src/cli/mod.rs
+++ b/src/cli/mod.rs
@@ -1,2 +1,3 @@
 pub mod clean;
 pub mod index;
+pub mod status;
diff --git a/src/cli/status.rs b/src/cli/status.rs
new file mode 100644
index 0000000..7807c63
--- /dev/null
+++ b/src/cli/status.rs
@@ -0,0 +1,147 @@
+use std::fmt;
+use std::io::Write;
+use std::path::{Path, PathBuf};
+
+use clap::ValueEnum;
+use serde::Serialize;
+use walkdir::WalkDir;
+
+use crate::indexer::state::{IndexState, StateError};
+use crate::output::strip_control_chars;
+
+/// status コマンドの出力フォーマット
+#[derive(Debug, Clone, Copy, ValueEnum)]
+pub enum StatusFormat {
+    Human,
+    Json,
+}
+
+/// status コマンドのエラー型
+#[derive(Debug)]
+pub enum StatusError {
+    State(StateError),
+    NotInitialized,
+    DirectoryNotFound(PathBuf),
+}
+
+impl fmt::Display for StatusError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            StatusError::State(e) => write!(f, "{e}"),
+            StatusError::NotInitialized => {
+                write!(f, "Index not initialized. Run `commandindex index` first.")
+            }
+            StatusError::DirectoryNotFound(p) => {
+                write!(f, "Directory not found: {}", p.display())
+            }
+        }
+    }
+}
+
+impl std::error::Error for StatusError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            StatusError::State(e) => Some(e),
+            _ => None,
+        }
+    }
+}
+
+impl From<StateError> for StatusError {
+    fn from(e: StateError) -> Self {
+        StatusError::State(e)
+    }
+}
+
+/// status コマンドの出力情報
+#[derive(Debug, Serialize)]
+pub struct StatusInfo {
+    #[serde(flatten)]
+    pub state: IndexState,
+    pub index_size_bytes: u64,
+}
+
+/// ディレクトリサイズを再帰的に計算する
+///
+/// エラーが発生したエントリはスキップし、取得可能なファイルサイズの合計を返す。
+pub fn compute_dir_size(dir: &Path) -> u64 {
+    WalkDir::new(dir)
+        .follow_links(false)
+        .max_depth(10)
+        .into_iter()
+        .filter_map(|e| e.ok())
+        .filter(|e| e.file_type().is_file())
+        .map(|e| e.metadata().map(|m| m.len()).unwrap_or(0))
+        .sum()
+}
+
+/// バイト数を人間が読みやすい形式にフォーマットする
+pub fn format_size(bytes: u64) -> String {
+    const KB: u64 = 1024;
+    const MB: u64 = 1024 * 1024;
+    const GB: u64 = 1024 * 1024 * 1024;
+
+    if bytes >= GB {
+        format!("{:.1} GB", bytes as f64 / GB as f64)
+    } else if bytes >= MB {
+        format!("{:.1} MB", bytes as f64 / MB as f64)
+    } else if bytes >= KB {
+        format!("{:.1} KB", bytes as f64 / KB as f64)
+    } else {
+        format!("{bytes} B")
+    }
+}
+
+/// status コマンドのメインロジック
+pub fn run(path: &Path, format: StatusFormat, writer: &mut dyn Write) -> Result<(), StatusError> {
+    if !path.is_dir() {
+        return Err(StatusError::DirectoryNotFound(path.to_path_buf()));
+    }
+
+    let commandindex_dir = path.join(".commandindex");
+
+    if !IndexState::exists(&commandindex_dir) {
+        return Err(StatusError::NotInitialized);
+    }
+
+    let state = IndexState::load(&commandindex_dir)?;
+    state.check_schema_version()?;
+
+    let index_size_bytes = compute_dir_size(&commandindex_dir);
+
+    let info = StatusInfo {
+        state,
+        index_size_bytes,
+    };
+
+    match format {
+        StatusFormat::Human => {
+            let index_root = strip_control_chars(&info.state.index_root.display().to_string());
+            writeln!(writer, "CommandIndex Status").ok();
+            writeln!(writer, "  Index root:    {index_root}").ok();
+            writeln!(writer, "  Version:       {}", info.state.version).ok();
+            writeln!(writer, "  Created:       {} UTC", info.state.created_at).ok();
+            writeln!(
+                writer,
+                "  Last updated:  {} UTC",
+                info.state.last_updated_at
+            )
+            .ok();
+            writeln!(writer, "  Total files:   {}", info.state.total_files).ok();
+            writeln!(writer, "  Total sections: {}", info.state.total_sections).ok();
+            writeln!(
+                writer,
+                "  Index size:    {}",
+                format_size(info.index_size_bytes)
+            )
+            .ok();
+        }
+        StatusFormat::Json => {
+            let json = serde_json::to_string_pretty(&info)
+                .map_err(|e| StatusError::State(StateError::Json(e)))?;
+            writeln!(writer, "{json}").ok();
+        }
+    }
+
+    Ok(())
+}
diff --git a/src/main.rs b/src/main.rs
index 58e2f9f..6a13d67 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -31,7 +31,14 @@ enum Commands {
     /// Incrementally update the index
     Update,
     /// Show index status
-    Status,
+    Status {
+        /// Target directory
+        #[arg(long, default_value = ".")]
+        path: PathBuf,
+        /// Output format (human, json)
+        #[arg(long, value_enum, default_value_t = commandindex::cli::status::StatusFormat::Human)]
+        format: commandindex::cli::status::StatusFormat,
+    },
     /// Remove index and prepare for rebuild
     Clean {
         /// Target directory containing .commandindex/
@@ -71,9 +78,14 @@ fn main() {
             eprintln!("Error: `update` command is not yet implemented. Coming in Phase 2.");
             1
         }
-        Commands::Status => {
-            eprintln!("Error: `status` command is not yet implemented. Coming in Phase 1.");
-            1
+        Commands::Status { path, format } => {
+            match commandindex::cli::status::run(&path, format, &mut std::io::stdout()) {
+                Ok(()) => 0,
+                Err(e) => {
+                    eprintln!("{e}");
+                    1
+                }
+            }
         }
         Commands::Clean { path } => match commandindex::cli::clean::run(&path) {
             Ok(commandindex::cli::clean::CleanResult::Removed) => {
diff --git a/tests/cli_args.rs b/tests/cli_args.rs
index 487b0f9..dacc5e3 100644
--- a/tests/cli_args.rs
+++ b/tests/cli_args.rs
@@ -60,14 +60,6 @@ fn update_subcommand_exits_with_not_implemented() {
         .stderr(predicate::str::contains("not yet implemented"));
 }
 
-#[test]
-fn status_subcommand_exits_with_not_implemented() {
-    common::cmd()
-        .arg("status")
-        .assert()
-        .failure()
-        .stderr(predicate::str::contains("not yet implemented"));
-}
 
 #[test]
 fn search_requires_query_argument() {
diff --git a/tests/cli_status.rs b/tests/cli_status.rs
new file mode 100644
index 0000000..882bbb4
--- /dev/null
+++ b/tests/cli_status.rs
@@ -0,0 +1,197 @@
+mod common;
+
+use std::io::Cursor;
+use std::path::PathBuf;
+
+use commandindex::cli::status::{StatusFormat, compute_dir_size, format_size, run};
+
+// ===== format_size tests =====
+
+#[test]
+fn format_size_bytes() {
+    assert_eq!(format_size(0), "0 B");
+    assert_eq!(format_size(512), "512 B");
+    assert_eq!(format_size(1023), "1023 B");
+}
+
+#[test]
+fn format_size_kilobytes() {
+    assert_eq!(format_size(1024), "1.0 KB");
+    assert_eq!(format_size(1536), "1.5 KB");
+    assert_eq!(format_size(1024 * 1023), "1023.0 KB");
+}
+
+#[test]
+fn format_size_megabytes() {
+    assert_eq!(format_size(1024 * 1024), "1.0 MB");
+    assert_eq!(format_size(1024 * 1024 * 500), "500.0 MB");
+}
+
+#[test]
+fn format_size_gigabytes() {
+    assert_eq!(format_size(1024 * 1024 * 1024), "1.0 GB");
+    assert_eq!(format_size(1024 * 1024 * 1024 * 2), "2.0 GB");
+}
+
+// ===== compute_dir_size tests =====
+
+#[test]
+fn compute_dir_size_empty_dir() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    let size = compute_dir_size(dir.path());
+    assert_eq!(size, 0);
+}
+
+#[test]
+fn compute_dir_size_with_files() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    std::fs::write(dir.path().join("a.txt"), "hello").expect("write file");
+    std::fs::write(dir.path().join("b.txt"), "world!").expect("write file");
+    let size = compute_dir_size(dir.path());
+    assert_eq!(size, 11); // 5 + 6
+}
+
+#[test]
+fn compute_dir_size_nested() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    let sub = dir.path().join("sub");
+    std::fs::create_dir(&sub).expect("create subdir");
+    std::fs::write(sub.join("file.txt"), "abc").expect("write file");
+    let size = compute_dir_size(dir.path());
+    assert_eq!(size, 3);
+}
+
+// ===== run() error cases =====
+
+#[test]
+fn run_directory_not_found() {
+    let mut buf = Cursor::new(Vec::new());
+    let path = PathBuf::from("/nonexistent/path/that/does/not/exist");
+    let result = run(&path, StatusFormat::Human, &mut buf);
+    assert!(result.is_err());
+    let err_msg = result.unwrap_err().to_string();
+    assert!(err_msg.contains("Directory not found"));
+}
+
+#[test]
+fn run_not_initialized() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    let mut buf = Cursor::new(Vec::new());
+    let result = run(dir.path(), StatusFormat::Human, &mut buf);
+    assert!(result.is_err());
+    let err_msg = result.unwrap_err().to_string();
+    assert!(err_msg.contains("not initialized"));
+}
+
+// ===== run() success cases =====
+
+fn setup_commandindex_dir(base: &std::path::Path) {
+    let ci_dir = base.join(".commandindex");
+    std::fs::create_dir_all(&ci_dir).expect("create .commandindex");
+
+    let state = commandindex::indexer::state::IndexState::new(base.to_path_buf());
+    state.save(&ci_dir).expect("save state");
+}
+
+#[test]
+fn run_human_format() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    setup_commandindex_dir(dir.path());
+
+    let mut buf = Cursor::new(Vec::new());
+    run(dir.path(), StatusFormat::Human, &mut buf).expect("run should succeed");
+
+    let output = String::from_utf8(buf.into_inner()).expect("valid utf8");
+    assert!(output.contains("CommandIndex Status"));
+    assert!(output.contains("Index root:"));
+    assert!(output.contains("Version:"));
+    assert!(output.contains("Created:"));
+    assert!(output.contains("Last updated:"));
+    assert!(output.contains("Total files:"));
+    assert!(output.contains("Total sections:"));
+    assert!(output.contains("Index size:"));
+}
+
+#[test]
+fn run_json_format() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    setup_commandindex_dir(dir.path());
+
+    let mut buf = Cursor::new(Vec::new());
+    run(dir.path(), StatusFormat::Json, &mut buf).expect("run should succeed");
+
+    let output = String::from_utf8(buf.into_inner()).expect("valid utf8");
+    let parsed: serde_json::Value = serde_json::from_str(&output).expect("valid json");
+    assert!(parsed.get("version").is_some());
+    assert!(parsed.get("total_files").is_some());
+    assert!(parsed.get("total_sections").is_some());
+    assert!(parsed.get("index_size_bytes").is_some());
+    assert!(parsed.get("index_root").is_some());
+    assert!(parsed.get("created_at").is_some());
+    assert!(parsed.get("last_updated_at").is_some());
+}
+
+// ===== E2E tests via CLI binary =====
+
+#[test]
+fn status_cli_not_initialized() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    common::cmd()
+        .args(["status", "--path", dir.path().to_str().unwrap()])
+        .assert()
+        .failure()
+        .stderr(predicates::prelude::predicate::str::contains(
+            "not initialized",
+        ));
+}
+
+#[test]
+fn status_cli_human_format() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    // First, run index to create .commandindex
+    common::cmd()
+        .args(["index", "--path", dir.path().to_str().unwrap()])
+        .assert()
+        .success();
+
+    common::cmd()
+        .args(["status", "--path", dir.path().to_str().unwrap()])
+        .assert()
+        .success()
+        .stdout(predicates::prelude::predicate::str::contains(
+            "CommandIndex Status",
+        ));
+}
+
+#[test]
+fn status_cli_json_format() {
+    let dir = tempfile::tempdir().expect("create temp dir");
+    // First, run index to create .commandindex
+    common::cmd()
+        .args(["index", "--path", dir.path().to_str().unwrap()])
+        .assert()
+        .success();
+
+    common::cmd()
+        .args([
+            "status",
+            "--path",
+            dir.path().to_str().unwrap(),
+            "--format",
+            "json",
+        ])
+        .assert()
+        .success()
+        .stdout(predicates::prelude::predicate::str::contains("\"version\""));
+}
+
+#[test]
+fn status_cli_directory_not_found() {
+    common::cmd()
+        .args(["status", "--path", "/nonexistent/dir"])
+        .assert()
+        .failure()
+        .stderr(predicates::prelude::predicate::str::contains(
+            "Directory not found",
+        ));
+}