He is remembered as the co-discoverer of the infectious agent of bubonic plague in Hong Kong in 1894 , simultaneously with Alexandre Yersin. Initially the bacillus was called Pasteurella pestis it is now called Yersinia pestis.
Born on Kyushu. He was educated at Kumamoto Medical School and Imperial University. He worked with Robert Koch in Germany (1885-91), and with Emil von Behring he was the first to grow the tetanus bacillus in pure culture and developed (1890) anti-toxins for diphtheria and anthrax. After returning to Japan in 1891 he founded an institute for the study of infectious diseases. When this was incorporated into Tokyo (ex-Imperial) University in 1914, he resigned and founded the Kitasato Institute, which he headed for the rest of his life.