The Republic's Cup 1931 was the 31st staging of the Copa del Rey, the Spanish football cup competition.

With the proclamation of the Second Spanish Republic on April 14, all teams with "Real" ("Royal") in their names, changed it due to anti-monarchic reasons. Real Sociedad changes to Donostia FC. Most of this changes were done between first and second legs of the first round.

The competition started on April 12, 1931, and concluded on June 21, 1931, with the final, held at the Estadio Chamartín in Madrid. Athletic Bilbao won their 11th title, the second in a row.

• Andalusia: Sevilla FC, Betis Balompié
• Aragon: Iberia SC, Patria Aragón
• Asturias: Oviedo FC, Sporting de Gijón
• Balearic Islands: RCD Mallorca
• Cantabria: Racing de Santander, Eclipse FC
• Castile and León: Cultural y Deportiva Leonesa, Valladolid Deportivo
• Catalonia: FC Barcelona, CD Sabadell, FC Badalona
• Extremadura: Don Benito FC
• Galicia: Celta de Vigo, Deportivo La Coruña
• Gipuzkoa: Unión Club, Donostia FC, CD Logroño
• Murcia: Murcia FC, Lorca FC
• Center Region: Madrid CF, Athletic Madrid, Racing de Madrid
• Valencia: Valencia CF, CD Castellón
• Biscay: Athletic Bilbao, CD Alavés, Arenas Club

The first leg was played on April 12. The second leg was played on May 3.

Athletic Bilbao and Sporting Gijón received a bye.

The first leg was played on May 10. The second leg was played on May 17.

• Tiebreaker

Played in Madrid on May 19.

The first leg was played on May 24. The second leg was played on May 31.

• Tiebreaker

Played in Barcelona on June 2.

The first leg was played on June 7. The second leg was played on June 14.

• Tiebreaker

Played in Madrid on June 16.