diff --git a/build.go b/build.go
index 45ae702..b03afe6 100644
--- a/build.go
+++ b/build.go
@@ -341,6 +341,12 @@ func (b *builder) processFunction(root *functionNode, props *builderProp) (query
 
 	var qyOutput query
 	switch root.FuncName {
+	case "lower-case":
+		arg, err := b.processNode(root.Args[0], flagsEnum.None, props)
+		if err != nil {
+			return nil, err
+		}
+		qyOutput = &functionQuery{Input: arg, Func: lowerCaseFunc}
 	case "starts-with":
 		arg1, err := b.processNode(root.Args[0], flagsEnum.None, props)
 		if err != nil {
diff --git a/func.go b/func.go
index 4131bfd..65386f0 100644
--- a/func.go
+++ b/func.go
@@ -645,3 +645,9 @@ func stringJoinFunc(arg1 query) func(query, iterator) interface{} {
 		return strings.Join(parts, separator)
 	}
 }
+
+// lower-case is XPATH function that converts a string to lower case.
+func lowerCaseFunc(q query, t iterator) interface{} {
+	v := functionArgs(q).Evaluate(t)
+	return strings.ToLower(asString(t, v))
+}
diff --git a/xpath_function_test.go b/xpath_function_test.go
index aed0824..06687ae 100644
--- a/xpath_function_test.go
+++ b/xpath_function_test.go
@@ -231,6 +231,13 @@ func Test_func_normalize_space(t *testing.T) {
 	test_xpath_eval(t, book_example, `normalize-space(//book[1]/title)`, "Everyday Italian")
 }
 
+func Test_func_lower_case(t *testing.T) {
+	test_xpath_eval(t, empty_example, `lower-case("ABc!D")`, "abc!d")
+	test_xpath_count(t, employee_example, `//name[@from="ca"]`, 0)
+	test_xpath_elements(t, employee_example, `//name[lower-case(@from) = "ca"]`, 9)
+	//test_xpath_eval(t, employee_example, `//employee/name/lower-case(text())`, "opal kole", "max miller", "beccaa moss")
+}
+
 func Benchmark_NormalizeSpaceFunc(b *testing.B) {
 	b.ReportAllocs()
 	const strForNormalization = "\t    \rloooooooonnnnnnngggggggg  \r \n tes  \u00a0 t strin \n\n \r g "