Seaweed meals have been widely used in the foods, dental materials, and pharmaceuticals in the early Eastern world, particularly in Japan as to be found in the Japanese classical literature. It is considerable important to briefly study the utilization of marine algae and the precise food scientific function of the chemical constituents in the algae, however, is unknown. The present paper deals with the development of useful and reliable methods for the potential utilization of the seaweed meals. Prasiola has a world-wide distribution and Prasiola japonica YATABE (Kawanori) grows on rock surfaces in mountain streams of rivers flowing into the Pacific Ocean extending from Kanto to Kyushu districts in Japan, being terrestrial as well as aquatic. The seasonal variation of constituents such as sterol, hydrocarbon, higher fatty acid, and phytol fractions from Prasiola japonica YATABE was examined. The contents of campesterol and stigmasterol varied in a relatively parallel way during all seasons. They appeaed to attain their maximum levels during the winter months, while the cholesterol and phytol contents were consistently low in all seasons. cis-7- Heptadecene was characteristically present in appreciable amounts except during the summer months. Conversely, CIs-unsaturated fatty acids rapidely increased from early summer to August and then rapidly decreased to a negligible amount in the winter months. The correlation between the seasonal variation of these constituents and the practical utilization for food is discussed. More information related to the biological role and the nutritive character of these components is needed to suggest future research problems.