SM UC-100 was a German Type UC III minelaying submarine or U-boat in the German Imperial Navy () during World War I.
A Type UC III submarine, UC-100 had a displacement of when at the surface and while submerged. She had a length overall of , a beam of , and a draught of . The submarine was powered by two six-cylinder four-stroke diesel engines each producing (a total of ), two electric motors producing , and two propeller shafts. She had a dive time of 15 seconds and was capable of operating at a depth of .
The submarine was designed for a maximum surface speed of and a submerged speed of . When submerged, she could operate for at ; when surfaced, she could travel at . UC-100 was fitted with six mine tubes, fourteen UC 200 mines, three torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one SK L/45 or Uk L/30 deck gun . Her complement was twenty-six crew members.
The U-boat was ordered on January 12, 1916, and was launched on April 14, 1918. She was commissioned into the German Imperial Navy on September 30, 1918, as SM UC-100. As with the rest of the completed UC III boats, UC-100 conducted no war patrols and sank no ships. She was surrendered to France on November 22, 1918, and was broken up in Cherbourg in July 1921.