East Sea or Eastern Sea may refer to:
- Sea of Japan, a marginal sea between Japanese archipelago, Russia, and Korean Peninsula. Called (Chosŏn) Tonghae ((조선)동해) in Korean, meaning "(Korean) East Sea". See: Sea of Japan naming dispute
- East China Sea, a marginal sea east of China, where it is called Dōng Hǎi (东海/東海) in Chinese, meaning "East Sea"
- South China Sea, a marginal sea south of China and east and south of Indochina, called Biển Đông in Vietnamese, meaning "East Sea"
- Baltic Sea, called "East Sea" in various languages
- Dead Sea, a salt lake east of Israel, as used in the Bible (Joel 2:20; Ezek. 47:18)
- Mare Orientale, Latin for "Eastern Sea", on the Moon
- Atlantic Ocean is also referred to as the East Sea or Eastern Sea, in poetry and other uses in North America
- Pacific Ocean is also called the East Sea in poetry and other uses from Australia, New Zealand, China and Japan