The seasonal variation of chemical constituents of baby clam (Paphia philippinarum) which was caught on the coast of the Ariake Bay, Fukuoka Prefecture, Kyushu, has been studied twice a month for two years, from March, 1946 to March, 1948. Total weight and shell weight were influenced only by variation of mean length of shell and did not exhibit seasonal variation, but muscle weight did. Degree of corpulency (Dry muscle weight
Total weight × 100) which was affected by season, changed reversely to the water existing in muscle and that existing; between shell and muscle. Muscle became corpulent in March and June. Seasonal influence upon ash-and crude fat-contents was not clearly exhibited seasonal variation, changing reversely with each other, and the latter changed perallelly with the degree of corpulency, which means that corpulency and recovery after spawning depend upon the increase of total carbohydrate. By the seasonal variation of chemical constituents, it is inferred that the spawning of the baby clam on the coast of the Ariake Bay takes place several times from spring to autumn.