diff --git a/src/mckicad/tools/analysis.py b/src/mckicad/tools/analysis.py
index 1c8e370..6d22ed1 100644
--- a/src/mckicad/tools/analysis.py
+++ b/src/mckicad/tools/analysis.py
@@ -6,6 +6,7 @@ detail retrieval into a single module. Uses KiCad IPC when available
 for live data, falling back to file-based checks otherwise.
 """
 
+import glob
 import json
 import logging
 import os
@@ -188,15 +189,13 @@ def validate_project(project_path: str) -> dict[str, Any]:
     except Exception as e:
         issues.append(f"Error reading project file: {e}")
 
-    # Validate schematic sexp integrity (all .kicad_sch files in project dir)
+    # Validate schematic sexp integrity (all .kicad_sch files, including sub-sheets)
     if "schematic" in files:
         project_dir = os.path.dirname(project_path)
-        sch_files = [
-            os.path.join(project_dir, f)
-            for f in os.listdir(project_dir)
-            if f.endswith(".kicad_sch")
-        ]
-        for sch_path in sorted(sch_files):
+        sch_files = sorted(
+            glob.glob(os.path.join(project_dir, "**", "*.kicad_sch"), recursive=True)
+        )
+        for sch_path in sch_files:
             issues.extend(_validate_schematic_sexp(sch_path))
 
     # Optional live analysis via KiCad IPC
diff --git a/tests/test_analysis.py b/tests/test_analysis.py
index b955798..aad210a 100644
--- a/tests/test_analysis.py
+++ b/tests/test_analysis.py
@@ -1,5 +1,6 @@
 """Tests for project analysis and validation tools."""
 
+import json
 import os
 import textwrap
 
@@ -134,3 +135,46 @@ class TestValidateSchematicSexp:
         path = self._write_sch(tmp_output_dir, "empty.kicad_sch", content)
         issues = _validate_schematic_sexp(path)
         assert issues == []
+
+    def test_subdirectory_sheets_scanned(self, tmp_output_dir):
+        """validate_project scans .kicad_sch files in subdirectories."""
+        from mckicad.tools.analysis import validate_project
+
+        # Create a minimal project structure with a sub-sheet in sheets/
+        pro_path = os.path.join(tmp_output_dir, "test.kicad_pro")
+        with open(pro_path, "w") as f:
+            json.dump({}, f)
+
+        # Root schematic — clean
+        root_sch = os.path.join(tmp_output_dir, "test.kicad_sch")
+        with open(root_sch, "w") as f:
+            f.write(textwrap.dedent("""\
+                (kicad_sch (version 20231120) (generator "eeschema")
+                  (lib_symbols)
+                )
+            """))
+
+        # Sub-sheet in sheets/ — has malformed property private
+        sheets_dir = os.path.join(tmp_output_dir, "sheets")
+        os.makedirs(sheets_dir)
+        sub_sch = os.path.join(sheets_dir, "sub.kicad_sch")
+        with open(sub_sch, "w") as f:
+            f.write(textwrap.dedent("""\
+                (kicad_sch (version 20231120) (generator "eeschema")
+                  (lib_symbols
+                    (symbol "Device:Crystal_GND24"
+                      (property "private" "KLC_S3.3" malformed
+                        (at 0 0 0)
+                        (effects (font (size 1.27 1.27)) (hide yes))
+                      )
+                    )
+                  )
+                )
+            """))
+
+        result = validate_project(pro_path)
+        # Should find the malformation in the sub-sheet
+        issues = result.get("issues") or []
+        sexp_issues = [i for i in issues if "private" in i]
+        assert len(sexp_issues) == 1
+        assert "sub.kicad_sch" in sexp_issues[0]