diff --git a/src/guardrails/agents.py b/src/guardrails/agents.py
index 0645081..a0c9168 100644
--- a/src/guardrails/agents.py
+++ b/src/guardrails/agents.py
@@ -451,6 +451,33 @@ async def stage_guardrail(ctx: RunContextWrapper[None], agent: Agent, input_data
     return guardrail_functions
 
 
+def _resolve_agent_instructions(instructions: str | None, prompt: Any | None) -> str | None:
+    """Derive instructions from explicit input or prompt.
+
+    Args:
+        instructions: Explicit instructions provided by the caller.
+        prompt: Optional prompt object or string supplied to the agent.
+
+    Returns:
+        A string containing the agent instructions when available, otherwise ``None``.
+    """
+    if instructions is not None:
+        return instructions
+
+    if prompt is None:
+        return None
+
+    if isinstance(prompt, str):
+        return prompt
+
+    for attr_name in ("instructions", "text", "content"):
+        candidate = getattr(prompt, attr_name, None)
+        if isinstance(candidate, str):
+            return candidate
+
+    return None
+
+
 class GuardrailAgent:
     """Drop-in replacement for Agents SDK Agent with automatic guardrails integration.
 
@@ -492,7 +519,7 @@ def __new__(
         cls,
         config: str | Path | dict[str, Any],
         name: str,
-        instructions: str,
+        instructions: str | None = None,
         raise_guardrail_errors: bool = False,
         block_on_tool_violations: bool = False,
         **agent_kwargs: Any,
@@ -511,7 +538,7 @@ def __new__(
         Args:
             config: Pipeline configuration (file path, dict, or JSON string)
             name: Agent name
-            instructions: Agent instructions
+            instructions: Agent instructions. When omitted, a ``prompt`` argument must be provided.
             raise_guardrail_errors: If True, raise exceptions when guardrails fail to execute.
                 If False (default), treat guardrail errors as safe and continue execution.
             block_on_tool_violations: If True, tool guardrail violations raise exceptions (halt execution).
@@ -614,5 +641,19 @@ def __new__(
                 )
                 _attach_guardrail_to_tools(tools, tool_output_gr, "output")
 
+        prompt_arg: Any | None = agent_kwargs.get("prompt")
+        resolved_instructions = _resolve_agent_instructions(instructions, prompt_arg)
+
+        if resolved_instructions is None and prompt_arg is None:
+            raise ValueError(
+                "GuardrailAgent requires either 'instructions' or 'prompt' to initialize the underlying Agent."
+            )
+
         # Create and return a regular Agent instance with guardrails configured
-        return Agent(name=name, instructions=instructions, input_guardrails=input_guardrails, output_guardrails=output_guardrails, **agent_kwargs)
+        return Agent(
+            name=name,
+            instructions=resolved_instructions,
+            input_guardrails=input_guardrails,
+            output_guardrails=output_guardrails,
+            **agent_kwargs,
+        )
diff --git a/tests/unit/test_agents.py b/tests/unit/test_agents.py
index 0aa1c4d..5725e19 100644
--- a/tests/unit/test_agents.py
+++ b/tests/unit/test_agents.py
@@ -6,13 +6,18 @@
 import types
 from collections.abc import Callable
 from dataclasses import dataclass
+from pathlib import Path
 from types import SimpleNamespace
 from typing import Any
 
 import pytest
 
-from guardrails._openai_utils import SAFETY_IDENTIFIER_HEADER, SAFETY_IDENTIFIER_VALUE
-from guardrails.types import GuardrailResult
+guardrails_pkg = types.ModuleType("guardrails")
+guardrails_pkg.__path__ = [str(Path(__file__).resolve().parents[2] / "src" / "guardrails")]
+sys.modules.setdefault("guardrails", guardrails_pkg)
+
+from guardrails._openai_utils import SAFETY_IDENTIFIER_HEADER, SAFETY_IDENTIFIER_VALUE  # noqa: E402
+from guardrails.types import GuardrailResult  # noqa: E402
 
 # ---------------------------------------------------------------------------
 # Stub agents SDK module so guardrails.agents can import required symbols.
@@ -94,7 +99,8 @@ class Agent:
     """Trivial Agent stub storing initialization args for assertions."""
 
     name: str
-    instructions: str
+    instructions: str | None = None
+    prompt: Any | None = None
     input_guardrails: list[Callable] | None = None
     output_guardrails: list[Callable] | None = None
     tools: list[Any] | None = None
@@ -597,3 +603,42 @@ def test_guardrail_agent_without_tools(monkeypatch: pytest.MonkeyPatch) -> None:
     agent_instance = agents.GuardrailAgent(config={}, name="NoTools", instructions="None")
 
     assert getattr(agent_instance, "input_guardrails", []) == []  # noqa: S101
+
+
+def test_guardrail_agent_allows_prompt_without_instructions(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Prompt attribute text becomes derived instructions."""
+    pipeline = SimpleNamespace(pre_flight=None, input=None, output=None)
+
+    monkeypatch.setattr(runtime_module, "load_pipeline_bundles", lambda config: pipeline, raising=False)
+    monkeypatch.setattr(runtime_module, "instantiate_guardrails", lambda *args, **kwargs: [], raising=False)
+
+    prompt = SimpleNamespace(text="Serve customers helpfully.")
+
+    agent_instance = agents.GuardrailAgent(config={}, name="PromptOnly", prompt=prompt)
+
+    assert agent_instance.prompt is prompt  # noqa: S101
+    assert agent_instance.instructions == "Serve customers helpfully."  # noqa: S101
+
+
+def test_guardrail_agent_accepts_string_prompt(monkeypatch: pytest.MonkeyPatch) -> None:
+    """String prompts populate missing instructions automatically."""
+    pipeline = SimpleNamespace(pre_flight=None, input=None, output=None)
+
+    monkeypatch.setattr(runtime_module, "load_pipeline_bundles", lambda config: pipeline, raising=False)
+    monkeypatch.setattr(runtime_module, "instantiate_guardrails", lambda *args, **kwargs: [], raising=False)
+
+    agent_instance = agents.GuardrailAgent(config={}, name="PromptStr", prompt="Be concise.")
+
+    assert agent_instance.prompt == "Be concise."  # noqa: S101
+    assert agent_instance.instructions == "Be concise."  # noqa: S101
+
+
+def test_guardrail_agent_requires_instructions_or_prompt(monkeypatch: pytest.MonkeyPatch) -> None:
+    """GuardrailAgent requires instructions or prompt for construction."""
+    pipeline = SimpleNamespace(pre_flight=None, input=None, output=None)
+
+    monkeypatch.setattr(runtime_module, "load_pipeline_bundles", lambda config: pipeline, raising=False)
+    monkeypatch.setattr(runtime_module, "instantiate_guardrails", lambda *args, **kwargs: [], raising=False)
+
+    with pytest.raises(ValueError):
+        agents.GuardrailAgent(config={}, name="Missing")