Isamu Masuda (?? ?, Masuda Isamu, December 25, 1872 – March 10, 1945) was a pioneering Japanese physician who studied the treatment of leprosy.
Studying in Aomori and Yokohama in his hospital, he wrote a book Leprosy and Social Problems in 1907, the year of the promulgation of the first leprosy law, and openly criticized the crucial segregation policy.
He advocated the nation's involvement in the discovery of treatments of leprosy, since he believed that it was curable.