diff --git a/CHANGELOG-3.6.md b/CHANGELOG-3.6.md
index 03f13319f..2560e0578 100644
--- a/CHANGELOG-3.6.md
+++ b/CHANGELOG-3.6.md
@@ -41,6 +41,7 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.5.0...v3.6.0).
 - Fix [Lease checkpoints don't prevent to reset ttl on leader change](https://github.com/etcd-io/etcd/pull/13508).
 - Fix [assertion failed due to tx closed when recovering v3 backend from a snapshot db](https://github.com/etcd-io/etcd/pull/13500)
 - Fix [A client can panic etcd by passing invalid utf-8 in the client-api-version header](https://github.com/etcd-io/etcd/pull/13560)
+- Fix [etcd gateway doesn't format the endpoint of IPv6 address correctly](https://github.com/etcd-io/etcd/pull/13551)
 
 ### tools/benchmark
 
diff --git a/server/proxy/tcpproxy/userspace.go b/server/proxy/tcpproxy/userspace.go
index 81421bffa..4df69aca8 100644
--- a/server/proxy/tcpproxy/userspace.go
+++ b/server/proxy/tcpproxy/userspace.go
@@ -19,6 +19,7 @@ import (
 	"io"
 	"math/rand"
 	"net"
+	"strings"
 	"sync"
 	"time"
 
@@ -69,13 +70,29 @@ type TCPProxy struct {
 	pickCount int // for round robin
 }
 
+// The parameter host is returned by net.SplitHostPort previously,
+// so it must be a valid host. This function is only to check whether
+// it's an IPv6 IP address.
+func isIPv6(host string) bool {
+	return strings.IndexRune(host, ':') != -1
+}
+
+// A literal IPv6 address in hostport must be enclosed in square
+// brackets, as in "[::1]:80", "[::1%lo0]:80".
+func formatAddr(host string, port uint16) string {
+	if isIPv6(host) {
+		return fmt.Sprintf("[%s]:%d", host, port)
+	}
+	return fmt.Sprintf("%s:%d", host, port)
+}
+
 func (tp *TCPProxy) Run() error {
 	tp.donec = make(chan struct{})
 	if tp.MonitorInterval == 0 {
 		tp.MonitorInterval = 5 * time.Minute
 	}
 	for _, srv := range tp.Endpoints {
-		addr := fmt.Sprintf("%s:%d", srv.Target, srv.Port)
+		addr := formatAddr(srv.Target, srv.Port)
 		tp.remotes = append(tp.remotes, &remote{srv: srv, addr: addr})
 	}
 
diff --git a/server/proxy/tcpproxy/userspace_test.go b/server/proxy/tcpproxy/userspace_test.go
index 2b98cd004..892e87eb8 100644
--- a/server/proxy/tcpproxy/userspace_test.go
+++ b/server/proxy/tcpproxy/userspace_test.go
@@ -129,3 +129,34 @@ func TestUserspaceProxyPriority(t *testing.T) {
 		t.Errorf("got = %s, want %s", got, want)
 	}
 }
+
+func TestFormatAddr(t *testing.T) {
+	addrs := []struct {
+		host         string
+		port         uint16
+		expectedAddr string
+	}{
+		{
+			"192.168.1.10",
+			2379,
+			"192.168.1.10:2379",
+		},
+		{
+			"::1",
+			2379,
+			"[::1]:2379",
+		},
+		{
+			"2001:db8::ff00:42:8329",
+			80,
+			"[2001:db8::ff00:42:8329]:80",
+		},
+	}
+
+	for _, addr := range addrs {
+		actualAddr := formatAddr(addr.host, addr.port)
+		if actualAddr != addr.expectedAddr {
+			t.Errorf("actualAddr: %s, expectedAddr: %s", actualAddr, addr.expectedAddr)
+		}
+	}
+}