The purpose of this paper is to discuss the origins of molecular biology in Japan. Japanese molecular biology does not have a long history since it started only after World War II. Especially, molecular genetics which uses "bacteriophage" had hardly been studied before the war and only a few scientists were interested in it immediately after the war. This is one of the origins of molecular biology in Japan. But there are other origins, one of which is the group formed by biologists, biochemists and physicists interested in nucleic acids. This group also started just after the war. Still another origin is the group of enzymologists. Enzymology was one of the main subjects of biochemistry from before the war. In Japan, biochemistry developed in conjunction with the medical and agricultural sciences from the pre-war era. These played an important role in introducing molecular biology from Europe and the United States after the war. A historical study of the development of molecular biology in Japan, comparing it with the history of molecular biology in Europe and the United States, should contribute to the elucidation of the features of the history of molecular biology in Japan.