Masaki Sewaga graduated from the Tokyo Medical University (1882).
Masaki Sewaga was a physician in ordinary to the Lord of Takatsuki Clan. He became an instructor, then director of the Miyagi Medial School. Upon closing of the school (1888), he went to Germany and studied pediatrics.
Returning home (1891), he was appointed professor at the Chiba Medical College and chief of its internal disease section. Resigning from the post (1898), he established the Koto Hospital for children in Tokyo. He established the Tokyo Pediatrics Hospital in Kanda (1910). Became concurrently director of the Minami-Katsushika Hospital. Wrote books on pediatrics and child care.