Kaisei Academy (Japanese: 開成学園, Kaisei Gakuen) is a private secondary school for boys located in Arakawa, Tokyo.

The school's motto is a tradition of 質実剛健 (shitsujitsugouken), a yojijukugo Japanese phrase meaning “strong and simple”.

Its English motto is "The pen is mightier than the sword".

The school was founded in 1871 by Sano Kanae, a lecturer of Western studies, gunnery, and oceanography.

[2] Initially established as Kyōryū Academy (共立学校), the school was closed after Sano's death in 1877.