diff --git a/NEWS b/NEWS
index 01f8af8ac8e..afb437984b3 100644
--- a/NEWS
+++ b/NEWS
@@ -29,6 +29,10 @@ PHP                                                                        NEWS
   . Fixed bug #80889 (Cannot set save handler when save_handler is invalid).
     (cmb)
 
+- SOAP:
+  . Fixed bug #69668 (SOAP special XML characters in namespace URIs not
+    encoded). (cmb)
+
 01 Apr 2021, PHP 8.0.4
 
 - Core:
diff --git a/ext/soap/php_encoding.c b/ext/soap/php_encoding.c
index b3dd853298f..f5723e213a4 100644
--- a/ext/soap/php_encoding.c
+++ b/ext/soap/php_encoding.c
@@ -3379,6 +3379,7 @@ xmlNsPtr encode_add_ns(xmlNodePtr node, const char* ns)
 		} else {
 			smart_str prefix = {0};
 			int num = ++SOAP_GLOBAL(cur_uniq_ns);
+			xmlChar *enc_ns;
 
 			while (1) {
 				smart_str_appendl(&prefix, "ns", 2);
@@ -3392,7 +3393,9 @@ xmlNsPtr encode_add_ns(xmlNodePtr node, const char* ns)
 				num = ++SOAP_GLOBAL(cur_uniq_ns);
 			}
 
-			xmlns = xmlNewNs(node->doc->children, BAD_CAST(ns), BAD_CAST(prefix.s ? ZSTR_VAL(prefix.s) : ""));
+			enc_ns = xmlEncodeSpecialChars(node->doc, BAD_CAST(ns));
+			xmlns = xmlNewNs(node->doc->children, enc_ns, BAD_CAST(prefix.s ? ZSTR_VAL(prefix.s) : ""));
+			xmlFree(enc_ns);
 			smart_str_free(&prefix);
 		}
 	}
diff --git a/ext/soap/tests/bug69668.phpt b/ext/soap/tests/bug69668.phpt
new file mode 100644
index 00000000000..59b3aa648fc
--- /dev/null
+++ b/ext/soap/tests/bug69668.phpt
@@ -0,0 +1,26 @@
+--TEST--
+Bug #69668 (SOAP: special XML characters in namespace URIs not encoded)
+--SKIPIF--
+<?php
+require_once('skipif.inc');
+?>
+--FILE--
+<?php
+class MySoapClient extends SoapClient {
+    public function __doRequest($request, $location, $action, $version, $one_way = 0) {
+        echo $request, PHP_EOL;
+        return '';
+    }
+}
+
+$client = new MySoapClient(__DIR__ . '/bug69668.wsdl', [
+    'trace'      => true,
+    'exceptions' => true,
+    'cache_wsdl' => WSDL_CACHE_NONE,
+]);
+
+$client->test();
+?>
+--EXPECT--
+<?xml version="1.0" encoding="UTF-8"?>
+<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="http://localhost/69668.php?a=a&amp;b=b" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><ns1:test/></SOAP-ENV:Body></SOAP-ENV:Envelope>
diff --git a/ext/soap/tests/bug69668.wsdl b/ext/soap/tests/bug69668.wsdl
new file mode 100644
index 00000000000..675db1e3e4b
--- /dev/null
+++ b/ext/soap/tests/bug69668.wsdl
@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<definitions xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:tns="http://localhost/69668.php?a=a&amp;b=b" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
+    xmlns:soap-enc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:soap12="http://schemas.xmlsoap.org/wsdl/soap12/" name="TestService" targetNamespace="http://localhost/69668.php?a=a&amp;b=b">
+    <types>
+        <xsd:schema targetNamespace="http://localhost/69668.php?a=a&amp;b=b" />
+    </types>
+    <portType name="TestServicePort">
+        <operation name="test">
+            <documentation>test</documentation>
+            <input message="tns:testIn" />
+            <output message="tns:testOut" />
+        </operation>
+    </portType>
+    <binding name="TestServiceBinding" type="tns:TestServicePort">
+        <soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http" />
+        <operation name="test">
+            <soap:operation soapAction="http://localhost/69668.php?a=a&amp;b=b#test" />
+            <input>
+                <soap:body use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="http://localhost/69668.php?a=a&amp;b=b" />
+            </input>
+            <output>
+                <soap:body use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="http://localhost/69668.php?a=a&amp;b=b" />
+            </output>
+        </operation>
+    </binding>
+    <service name="TestServiceService">
+        <port name="TestServicePort" binding="tns:TestServiceBinding">
+            <soap:address location="http://localhost/69668.php?a=a&amp;b=b" />
+        </port>
+    </service>
+    <message name="testIn" />
+    <message name="testOut">
+        <part name="return" type="xsd:string" />
+    </message>
+</definitions>