he Kawasaki OH-1 (nickname: "Ninja") is a military scout/observation helicopter developed and manufactured by the Kawasaki Aerospace Company. The primary operator is the Japan Ground Self-Defense Force (JGSDF), who originally procured the OH-1 as a domestically produced successor to their existing OH-6D Loach fleet. The OH-1 has the distinction of being the first helicopter to be entirely produced in Japan.

In addition to its use as an observation helicopter, it can also be armed to directly participate in combat; such weapons include a limited quantity of air-to-air missiles for self-defense purposes. Several variants of the OH-1 have been proposed, these have included derivatives of the type to serve as an attack helicopter as well as an aborted project to develop a utility helicopter. As of March 2014, a total of 38 OH-1s have entered service with the JGSDF; so far these complement the existing OH-6Ds rather than replace them.

In December 2022, the Japanese government decided to replace 33 OH -1, 12 AH-64D, 47 AH-1S, and 26 U-125A with unmanned aerial vehicles. Japan plans to increase its defense budget from 1.24% of GDP in fiscal 2021 to around 2.0% within 10 years, and has decided to retire these helicopters and aircraft as part of an effort to spend its defense budget efficiently.