SM UC-31 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 29 August 1915 and was launched on 7 August 1916. She was commissioned into the German Imperial Navy on 2 September 1916 as SM UC-31. In 13 patrols UC-31 was credited with sinking 38 ships, either by torpedo or by mines laid. UC-31 was surrendered on 26 November 1918 and broken up at Canning Town in 1922.