Doomsday may refer to:
- Doomsday, a monstrous clone of Superman created by Project Cadmus;
- "The Doomsday Sanction", an episode of Justice League Unlimited.
- The Doomsday Magnet, a device built by Granny Goodness to attract the Fleischer's Comet.
- The Doomsday Thermal Reactor, an Atlantean weapon of last resort built and installed at the North Pole by Aquaman.