This paper explores the introduction of demography by the Department of Hygiene and Preventive Medicine at Keijō Imperial University 京城帝國大學. Assistant Professor Mizushima Haruo 水島治夫 led the introduction of demography into colonial Korea in the 1930s, while carrying out intensive interactions with his colleagues in the field of eugenics. Focusing particularly on the influences of eugenics on Mizushima’s demographic studies, this paper examines how demography was accepted by Japanese doctors who emphasized the practicality of medical research. Eugenics helped raise demography into a crucial field for the Japanese Empire by allowing it to calculate the vitality of the Japanese race 日本人の生命力 vis-a-vis other races. By analyzing how eugenics constructed the social meanings of demography, this paper will illuminate the process through which eugenics expanded its influence on medicine.