The Copa del Rey 1918 was the 18th staging of the Copa del Rey, the Spanish football cup competition. The competition started on 8 April 1918, and concluded on 2 May 1918 with the final, held at the O'Donnell in Madrid, in which Real Unión lifted the trophy for the first time (second time counting the trophy won by Racing de Irun in 1913) with a 2–0 victory over Madrid FC with Juan Legarreta netting both goals for Unión.

Teams

Quarter-finals

Recreativo de Huelva and Fortuna de Vigo received a bye to the semi-finals. Real Unión and Sporting Gijón played a single match at a neutral venue, instead of a two-legged tie.

First leg

Second leg

''RCD Español and Madrid CF won one match each. At that year, the goal difference was not taken into account. A replay match was played.''

Replay

Madrid FC advanced to the semi-finals

One-legged game

''This was a one-legged match, played on neutral ground. Real Unión advanced to the semi-finals.''

Semifinals

First leg

Second leg

Madrid FC won 2–0 on aggregate matches.

One-legged game

This was a one-legged match, played on neutral ground, and it was Real Unión who advanced to the final with a 4–1 win.

Final