Ōi (大井) was the fourth of five Kuma-class light cruiser, which served in the Imperial Japanese Navy during World War II. She was named after the Ōi River in Shizuoka prefecture, Japan. Designed as a command vessel for a destroyer squadron, she was converted into a torpedo cruiser with forty torpedo launch tubes in a plan abandoned by the Japanese Navy in 1942. During most of the Pacific War, she was used primarily as a fast troop transport and was sunk by a United States Navy submarine in 1944.

The Kuma-class light cruisers were a class of five light cruisers built for and operated by the Imperial Japanese Navy (IJN). The Kuma-class cruisers proved useful in combat operations ranging from the Aleutian Islands to the Indian Ocean throughout World War II.