diff --git a/kliff/dataset/extxyz.py b/kliff/dataset/extxyz.py
index c8a0e239..5364b90f 100644
--- a/kliff/dataset/extxyz.py
+++ b/kliff/dataset/extxyz.py
@@ -46,8 +46,22 @@ def read_extxyz(
         cell = _parse_key_value(line, "Lattice", "float", 9, filename)
         cell = np.reshape(cell, (3, 3))
 
-        # PBC
-        PBC = _parse_key_value(line, "PBC", "int", 3, filename)
+        # PBC integer (0, 1) or str ("T", "F")
+        PBC = _parse_key_value(line, "PBC", "str", 3, filename)
+        try:
+            PBC = [bool(int(i)) for i in PBC]
+        except ValueError:
+            tmp = []
+            for p in PBC:
+                if p.lower() == "t":
+                    tmp.append(True)
+                elif p.lower() == "f":
+                    tmp.append(False)
+                else:
+                    raise InputError(
+                        f"Invalid PBC value {p} at line 2 of file {filename}."
+                    )
+            PBC = tmp
 
         # energy is optional
         try:
@@ -125,6 +139,7 @@ def write_extxyz(
     energy: Optional[float] = None,
     forces: Optional[np.ndarray] = None,
     stress: Optional[List[float]] = None,
+    bool_as_str: bool = False,
 ):
     """
     Write configuration info to a file in extended xyz file_format.
@@ -139,6 +154,8 @@ def write_extxyz(
         forces: Nx3 array, forces on atoms; If `None`, not write to file
         stress: 1D array of size 6, stress on the cell in Voigt notation; If `None`,
             not write to file
+        bool_as_str: If `True`, write PBC as "T" or "F"; otherwise, write PBC as 1 or 0.
+
     """
 
     with open(filename, "w") as fout:
@@ -155,7 +172,10 @@ def write_extxyz(
                 else:
                     fout.write("{:.15g} ".format(item))
 
-        PBC = [int(i) for i in PBC]
+        if bool_as_str:
+            PBC = ["T" if i else "F" for i in PBC]
+        else:
+            PBC = [int(i) for i in PBC]
         fout.write('PBC="{} {} {}" '.format(PBC[0], PBC[1], PBC[2]))
 
         if energy is not None:
@@ -204,7 +224,7 @@ def _parse_key_value(
     Args:
         line: The string line.
         key: Keyword to parse.
-        dtype: Expected data type of value, `int` or `float`.
+        dtype: Expected data type of value, `int`, `float` or `str`.
         size: Expected size of value.
         filename: File name where the line comes from.
 
@@ -221,7 +241,7 @@ def _parse_key_value(
         else:
             value = value[value.index("=") + 1 :]
             value = value.lstrip(" ")
-            value += " "  # add an whitespace at end in case this is the last key
+            value += " "  # add a whitespace at end in case this is the last key
             value = value[: value.index(" ")]
         value = value.split()
     except Exception as e:
@@ -237,6 +257,8 @@ def _parse_key_value(
             value = [float(i) for i in value]
         elif dtype == "int":
             value = [int(i) for i in value]
+        elif dtype == "str":
+            pass
     except Exception as e:
         raise InputError(f"{e}.\nCorrupted {key} data at line 2 of file {filename}.")
 
diff --git a/tests/dataset/test_extxyz.py b/tests/dataset/test_extxyz.py
index 3dfbd581..d1d8280c 100644
--- a/tests/dataset/test_extxyz.py
+++ b/tests/dataset/test_extxyz.py
@@ -1,7 +1,34 @@
 import numpy as np
 import pytest
 
-from kliff.dataset.dataset import Configuration, Dataset
+from kliff.dataset.dataset import Configuration, Dataset, read_extxyz, write_extxyz
+
+
+def test_read_write_extxyz(test_data_dir, tmp_dir):
+    path = test_data_dir.joinpath("configs/MoS2/MoS2_energy_forces_stress.xyz")
+    cell, species, coords, PBC, energy, forces, stress = read_extxyz(path)
+
+    fname = "test.xyz"
+    write_extxyz(
+        fname,
+        cell,
+        species,
+        coords,
+        PBC,
+        energy,
+        forces,
+        stress,
+        bool_as_str=True,
+    )
+    cell1, species1, coords1, PBC1, energy1, forces1, stress1 = read_extxyz(fname)
+
+    assert np.allclose(cell, cell1)
+    assert species == species1
+    assert np.allclose(coords, coords1)
+    assert PBC == PBC1
+    assert energy == energy1
+    assert np.allclose(forces, forces1)
+    assert stress == stress1
 
 
 @pytest.mark.parametrize(