- Ubume (Japanese) – Ghosts of women who died in childbirth
- Uchek Langmeidong (Meitei mythology) – Semi human, semi hornbill creature
- Ukko (Finnish) – Finnish sky deity
- Uma-no-ashi (Japanese) – Horse's leg which dangles from a tree and kicks passersby
- Umibōzu (Japanese) – Ghost of drowned priest
- Umi-nyōbō (Japanese) – Female sea monster who steals fish
- Undead (Worldwide) – Dead that behave as if alive
- Underwater panther (Native American) – Feline water spirit
- Undine (Alchemy) – Water elemental
- Unhcegila (Lakota) – Dragon
- Unicorn (Medieval Bestiaries) – Horse-like creature with the legs of an antelope, the tail of a lion and a single magical healing horn.
- Unktehi (Lakota) – Serpentine rain spirit
- Unktehila (Lakota) – Reptilian water monster
- Upinis (Lithuanian) – River spirit
- Ur (Mandaean) – King of the World of Darkness, often portrayed as a dragon or snake
- Urayuli (Native American) – Hairy giant
- Uriaș (Romanian) – Giant
- Urmahlullu (Mesopotamian) – Lion-human hybrid guardian spirit
- Ushi-oni (Japanese) – Bull-headed monster
- Utukku (Akkadian) – ″Underworld messenger spirit″
- Uwan (Japanese) – Spirit that shouts to surprise people