Morio Kasai (葛西 森夫; September 29, 1922 – December 8, 2008) was a Japanese surgeon who had a strong interest in pediatric surgery. While Kasai went into practice at a time when pediatric surgery was not an established subspecialty, much of his clinical and research work was related to the surgical care of children. He is best known for devising a surgical procedure, the hepatoportoenterostomy, to address a life-threatening birth defect known as biliary atresia. The modern form of the operation is still known as the Kasai procedure.