SM UB-33 was a German Type UB II submarine or U-boat in the German Imperial Navy () during World War I. The U-boat was ordered on 22 July 1915 and launched on 5 December 1915. She was commissioned into the German Imperial Navy on 22 April 1916 as SM UB-33. The submarine sank thirteen ships, damaged two others, and took a further three as prizes in seventeen patrols.