The present investigations were carried out for the purpose of making clear the fundamental features of the seasonal variations in carrageenan content and its chemical composition. The samples, Chondrus ocellatus, were collected every month from the same locality on the coast of Haewundae from March, 1975 to February, 1976, and analyzed monthly to determine their carrageenan content, sulphate and 3,6-anhydro-D-galactose over a year period. En addition, some chemical characteristics were also tested on the fractions separated by the different concentrations of potassium chloride. In seasonal variation, the maximum carrageenan content occurred from summer through autumn, and the minimum in winter, especially in February. It is noted in the seasonal variations of the sulphate content of total carrageenan and three fractions that the maximums appreared in October and minimums in february. With seasonal variations of percent 3,6-anhydro-D-galactose of total carrageenan and three fractions, maximum values occur in June and minimum values in December. Seasonal variations in sulphate and 3,6-anhydro-D-galactose contents of the three fractions were on the whole similar in mode of variation, and there could be no substancial differences. Seeing seasonal variations in the sulphate and 3,6-anhydro-D-galactose contents of three fractions, carrageenan extracted from the algae gathered in spring shelved higher portion of fraction I than that gathered in autumn. In these respects, it seems that a more weakly gelling k-carrageenan exists in the spring than in the autumn.