diff --git a/doc/source/changes/version_0_30.rst.inc b/doc/source/changes/version_0_30.rst.inc
index dde69b6d3..c437fe0a9 100644
--- a/doc/source/changes/version_0_30.rst.inc
+++ b/doc/source/changes/version_0_30.rst.inc
@@ -231,3 +231,5 @@ Fixes
   of the API Reference (closes :issue:`698`).
 
 * fixed arithmetic operations between two sessions returning a nan value for each axis and group (closes :issue:`725`).
+
+* fixed dumping sessions with metadata using HDF format (closes :issue:`702`).
diff --git a/larray/core/metadata.py b/larray/core/metadata.py
index 1a7387f53..61821c091 100644
--- a/larray/core/metadata.py
+++ b/larray/core/metadata.py
@@ -168,11 +168,15 @@ def _convert_value(value):
         return Metadata([(key, _convert_value(value)) for key, value in zip(array.axes.labels[0], array.data)])
 
     # ---------- IO methods ----------
-    def to_hdf(self, hdfstore, key):
+    def to_hdf(self, hdfstore, key=None):
         if len(self):
-            hdfstore.get_storer(key).attrs.metadata = self
+            attrs = hdfstore.get_storer(key).attrs if key is not None else hdfstore.root._v_attrs
+            attrs.metadata = self
 
     @classmethod
-    def from_hdf(cls, hdfstore, key):
-        if 'metadata' in hdfstore.get_storer(key).attrs:
-            return hdfstore.get_storer(key).attrs.metadata
+    def from_hdf(cls, hdfstore, key=None):
+        attrs = hdfstore.get_storer(key).attrs if key is not None else hdfstore.root._v_attrs
+        if 'metadata' in attrs:
+            return attrs.metadata
+        else:
+            return None
diff --git a/larray/inout/hdf.py b/larray/inout/hdf.py
index 0ce326a9d..67a69c811 100644
--- a/larray/inout/hdf.py
+++ b/larray/inout/hdf.py
@@ -143,11 +143,13 @@ def _dump_item(self, key, value, *args, **kwargs):
             raise TypeError()
 
     def _read_metadata(self):
-        attrs = self.handle.get_node('')._v_attrs
-        return attrs.metadata if 'metadata' in attrs else Metadata()
+        metadata = Metadata.from_hdf(self.handle)
+        if metadata is None:
+            metadata = Metadata()
+        return metadata
 
     def _dump_metadata(self, metadata):
-        self.handle.get_node('')._v_attrs.metadata = metadata
+        metadata.to_hdf(self.handle)
 
     def close(self):
         self.handle.close()