The amino acids composition and nutritive values of pearl oyster proteins were examined. The amino acid score of pearl oyster proteins was 88. Growth rates of rats fed a pearl oyster diet were higher than those fed a casein diet. True digestibility of pearl oyster proteins was lower than that of casein. The nutritive values of pearl oyster proteins measured for rats were about the same as those of casein. The level of total plasma cholesterol in rats fed the pearl oyster diet was lower than that of those fed the casein diet. Pearl oyster was thus considered to be a useful protein source, which could control the accumulation of total plasma cholesterol.