An angle-adjustable stirrup assembly includes a connector, a stirrup, and a locking element. The connector includes a plate connected to a crossbow, a sleeve formed on a face of the plate, and recesses in an external face of the sleeve. The stirrup is pivotally connected to the sleeve and includes a first section, a second section in parallel to the first section, a slot in the first section, and a tread formed on the second section. The locking element includes an end pivotally connected to the stirrup and another end formed with a boss for insertion in a selected one of the recesses via the slot to keep the stirrup in a selected one of several angles relative to the connector.