diff --git a/base64_s390x.go b/base64_s390x.go
new file mode 100644
index 0000000..a2938e8
--- /dev/null
+++ b/base64_s390x.go
@@ -0,0 +1,10 @@
+// Copyright 2024 Sun Yimin. All rights reserved.
+// Use of this source code is governed by a BSD 3-Clause-style
+// license that can be found in the LICENSE file.
+
+//go:build !purego
+
+package base64
+
+//go:noescape
+func encodeAsm(dst, src []byte, lut *[16]byte) int
diff --git a/base64_s390x.s b/base64_s390x.s
new file mode 100644
index 0000000..c40fe58
--- /dev/null
+++ b/base64_s390x.s
@@ -0,0 +1,102 @@
+// Copyright 2024 Sun Yimin. All rights reserved.
+// Use of this source code is governed by a BSD 3-Clause-style
+// license that can be found in the LICENSE file.
+
+//go:build !purego
+
+#include "textflag.h"
+
+DATA base64_const<>+0x00(SB)/8, $0x0f0e0d0c0b0a0908 // enccoding, byte order
+DATA base64_const<>+0x08(SB)/8, $0x0706050403020100
+DATA base64_const<>+0x10(SB)/8, $0x0a0b090a07080607 // enccoding, reshufling
+DATA base64_const<>+0x18(SB)/8, $0x0405030401020001
+DATA base64_const<>+0x20(SB)/8, $0x1010010204080408 // STD LUT HI
+DATA base64_const<>+0x28(SB)/8, $0x1010101010101010
+DATA base64_const<>+0x30(SB)/8, $0x1511111111111111 // STD LUT LO
+DATA base64_const<>+0x38(SB)/8, $0x1111131A1B1B1B1A
+DATA base64_const<>+0x40(SB)/8, $0x00101304BFBFB9B9 // STD LUT ROLL
+DATA base64_const<>+0x48(SB)/8, $0x0000000000000000
+DATA base64_const<>+0x50(SB)/8, $0x1010010204080428 // URL LUT HI
+DATA base64_const<>+0x58(SB)/8, $0x1010101010101010
+DATA base64_const<>+0x60(SB)/8, $0x1511111111111111 // URL LUT LO
+DATA base64_const<>+0x68(SB)/8, $0x1111131B1B1A1B33
+DATA base64_const<>+0x70(SB)/8, $0x00001104BFBFE0B9 // URL LUT ROLL
+DATA base64_const<>+0x78(SB)/8, $0xB900000000000000
+DATA base64_const<>+0x80(SB)/8, $0x010203050607090a // RESHUFFLE MASK
+DATA base64_const<>+0x88(SB)/8, $0x0b0d0e0f00000000
+GLOBL base64_const<>(SB), (NOPTR+RODATA), $144
+
+#define REV_BYTES V0
+#define RESHUFFLE_MASK V1
+#define MULHI_CONST V2
+#define MULHI_MASK V3
+#define MULLO_CONST V4
+#define MULLO_MASK V5
+#define RANGE1_END V6
+#define RANGE0_END V7
+#define LUT V8
+#define ZERO V9
+
+#define X0 V10
+#define X1 V11
+#define X2 V12
+
+//func encodeAsm(dst, src []byte, lut *[16]byte) int
+TEXT ·encodeAsm(SB),NOSPLIT,$0
+	MOVD dst_base+0(FP), R1
+	MOVD src_base+24(FP), R2
+	MOVD src_len+32(FP), R3
+	MOVD lut+48(FP), R4
+	VL (R4), LUT
+
+	MOVD $base64_const<>(SB), R5
+	VLM (R5), REV_BYTES, RESHUFFLE_MASK
+	VREPIF 0x0fc0fc00, MULHI_MASK
+	VREPIF 0x04000040, MULHI_CONST
+	VREPIF 0x003F03F0, MULLO_MASK
+	VREPIF 0x01000010, MULLO_CONST
+	VREPIB 0x33, RANGE1_END
+	VREPIB 0x19, RANGE0_END
+	VZERO ZERO
+
+loop:
+	VL (R2), X0
+	VPERM X0, X0, RESHUFFLE_MASK, X0
+	VN X0, MULHI_MASK, X1
+	VMLHH(X1, MULHI_CONST, X1)
+	VN X0, MULLO_MASK, X2
+	VMLHW(X2, MULLO_CONST, X2)
+	VO X1, X2, X0
+
+	VSB RANGE1_END, X0, X1
+	VMXB ZERO, X1, X1
+
+	VECLB RANGE0_END, X0, X2
+	VMXB ZERO, X2, X2
+	VAB X2, X1, X1
+
+	VPERM LUT, LUT, X1, X2
+	VAB X2, X0, X0
+
+	VPERM X0, X0, REV_BYTES, X0
+	VST X0, (R1)
+
+	LAY 12(R1), R1
+	LAY 16(R2), R2
+	SUB $16, R3
+	CMPBGE R3, $48, loop
+
+	RET
+
+#undef RESHUFFLE_MASK
+#undef SHIFT_RIGHT_MASK
+#undef MULHI_MASK
+#undef SHIFT_LEFT_MASK
+#undef MULLO_MASK
+#undef RANGE1_END
+#undef RANGE0_END
+#undef LUT
+#undef ZERO
+#undef X0
+#undef X1
+#undef X2
diff --git a/base64_s390x_test.go b/base64_s390x_test.go
new file mode 100644
index 0000000..72f8354
--- /dev/null
+++ b/base64_s390x_test.go
@@ -0,0 +1,37 @@
+// Copyright 2024 Sun Yimin. All rights reserved.
+// Use of this source code is governed by a BSD 3-Clause-style
+// license that can be found in the LICENSE file.
+
+//go:build s390x && !purego
+
+package base64
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestStdEncodeAsm(t *testing.T) {
+	pairs := []testpair{
+		{"abcdefghijkl0000", "YWJjZGVmZ2hpamts"},
+		{"\x2b\xf7\xcc\x27\x01\xfe\x43\x97\xb4\x9e\xbe\xed\x5a\xcc\x70\x90", "K/fMJwH+Q5e0nr7t"},
+		{"abcdefghijklabcdefghijkl0000", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
+		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
+		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
+		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
+	}
+	for _, p := range pairs {
+		src := []byte(p.decoded)
+		expected := []byte(p.encoded)
+		dst := make([]byte, len(expected))
+
+		ret := encodeAsm(dst, src, &encodeStdLut)
+		if ret != len(expected) {
+			t.Errorf("should return %v, got %v", len(expected), ret)
+		}
+		if !bytes.Equal(dst, expected) {
+			t.Errorf("got %x, expected %x", dst, expected)
+		}
+
+	}
+}