The Copa del Rey 1921 was the 21st staging of the Copa del Rey, the Spanish football cup competition. The competition started on 9 April 1921, and concluded on 8 May 1921, with the Final, held at the San Mamés in Bilbao, in which Athletic Bilbao lifted the trophy for the eighth time with a 4–1 victory over Athletic Madrid thanks to two braces from José María Laca and Domingo Acedo.