In continuation of the previous work (The New Medical Journal, Vol. 12, No. 3, 111, 1969), the effects on the bactericidal activity against coli form group, on vitamin C content and ascorbate oxidase activity of the purple laver due to the $^{80}Co$ gamma-irradiation were studied. The results obtained are ; 1) After the 0.1m rad./hr. doses treatment of gamma-irradiation for 1 hours to the laver, the coli form group was being remarkably destoryed and after the application for 10 hours the coli form group was completely destroyed. 2) The content of vitamin C was gradually decreased during the gamma-irradiation to the laver. According to the sensory test, no changes in flavor nad color were indicated for 9-10 hours treatment. But, the loss of ascorbic was much than that of dehydroascorbic acid after 10-hour treatment. 3) And also, the ascorbate oxidase activity due to the irradiation waas conspicuously decreased.