SM UB-129 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 11 June 1918 as SM UB-129. UB-129 was lost 31 October 1918 in Fiume (45°19′N 14°26′E / 45.317°N 14.433°E) after the surrender of Austria-Hungary.