diff --git a/changelogs/unreleased/api_make_protected_boolean_type.yml b/changelogs/unreleased/api_make_protected_boolean_type.yml
new file mode 100644
index 00000000000..765edea6427
--- /dev/null
+++ b/changelogs/unreleased/api_make_protected_boolean_type.yml
@@ -0,0 +1,5 @@
+---
+title: 'API: change protected attribute type to Boolean'
+merge_request: 28766
+author:
+type: other
diff --git a/lib/api/variables.rb b/lib/api/variables.rb
index 38ff1b3d9cf..6c61392ed63 100644
--- a/lib/api/variables.rb
+++ b/lib/api/variables.rb
@@ -54,7 +54,7 @@ module API
       params do
         requires :key, type: String, desc: 'The key of the variable'
         requires :value, type: String, desc: 'The value of the variable'
-        optional :protected, type: String, desc: 'Whether the variable is protected'
+        optional :protected, type: Boolean, desc: 'Whether the variable is protected'
         optional :masked, type: Boolean, desc: 'Whether the variable is masked'
         optional :variable_type, type: String, values: Ci::Variable.variable_types.keys, desc: 'The type of variable, must be one of env_var or file. Defaults to env_var'
 
@@ -81,7 +81,7 @@ module API
       params do
         optional :key, type: String, desc: 'The key of the variable'
         optional :value, type: String, desc: 'The value of the variable'
-        optional :protected, type: String, desc: 'Whether the variable is protected'
+        optional :protected, type: Boolean, desc: 'Whether the variable is protected'
         optional :masked, type: Boolean, desc: 'Whether the variable is masked'
         optional :variable_type, type: String, values: Ci::Variable.variable_types.keys, desc: 'The type of variable, must be one of env_var or file'