Umibōzu (海坊主, "sea priest") is a paranormal phenomenon or yōkai from Japanese mythology. Other names include Umihōshi (海法師) or Uminyūdō (海入道).

Little is known of the origin of umibōzu but it is a sea-spirit and as such has multiple sightings throughout Japan. Usually, it appears to sailors on calm seas which quickly turn tumultuous. The umibōzu either breaks the ship on emergence or demands a bucket or barrel from the sailors and proceeds to drown them. The only safe way to escape from them is to give it a bottomless barrel and sail away while it is confused.