diff --git a/src/dcore/interaction.py b/src/dcore/interaction.py
index 782c2c8d..e021ff74 100644
--- a/src/dcore/interaction.py
+++ b/src/dcore/interaction.py
@@ -418,10 +418,16 @@ def _generate_umat_file(p: Dict):
         try:
             if os.path.splitext(file)[1] == ".npy":
                 umat = numpy.load(file)
-                assert umat.shape == u_shape, f"inconsistent shape: require {u_shape}, but {umat.shape} is given"
+                assert umat.shape == u_shape, f"inconsistent shape: require {u_shape}, but {umat.shape} is given."
             else:
                 umat_1d = numpy.loadtxt(file)
-                umat = umat_1d.reshape(u_shape)
+                if umat_1d.shape == (numpy.prod(u_shape),):  # real U
+                    umat = umat_1d.reshape(u_shape)
+                elif umat_1d.shape == (numpy.prod(u_shape), 2):  # complex U
+                    # float (norb^4, 2) -> complex (norb^4, 1) -> complex (norb,norb,norb,norb)
+                    umat = umat_1d.view(complex).reshape(u_shape)
+                else:
+                    raise Exception(f"inconsisten shape: require {(numpy.prod(u_shape),)} for real U or {(numpy.prod(u_shape), 2)} for complex U, but {umat_1d.shape} is given.")
         except Exception as e:
             print(f"\nError in reading file '{file}' for ish={ish}", file=sys.stderr)
             print(e, file=sys.stderr)