SM UB-90 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 21 March 1918 as SM UB-90.

On 16 October 1918, UB-90 was hit by a torpedo from HMS L12 at 57°55′N 10°27′E / 57.917°N 10.450°E / 57.917; 10.450 and sunk. All 38 crew members died in the event.

She was built by AG Vulcan of Hamburg and following just under a year of construction, launched at Hamburg on 12 February 1918. UB-90 was commissioned early the next year under the command of Oblt.z.S. Gottfried von Mayer. Like all Type UB III submarines, UB-90 carried 10 torpedoes and was armed with a 10.5 cm (4.13 in) deck gun. UB-90 would carry a crew of up to 3 officer and 31 men and had a cruising range of 7,120 nautical miles (13,190 km; 8,190 mi). UB-90 had a displacement of 510 t (500 long tons) while surfaced and 640 t (630 long tons) when submerged. Her engines enabled her to travel at 13 knots (24 km/h; 15 mph) when surfaced and 7.4 knots (13.7 km/h; 8.5 mph) when submerged.

Date	Name	Nationality	Tonnage	Fate
29 July 1918	Douro	Denmark	850	Captured as prize
3 October 1918	Eupion	United Kingdom	3,575	Sunk