SM UB-66 was a German Type UB III submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. She was commissioned into the German Imperial Navy on 1 August 1917 as SM UB-66. UB-66 was sunk by at 38°30′N 24°25′E / 38.500°N 24.417°E on 18 January 1918, 30 crew members died in the event.