This paper presents the variation in lipid compositions during the ovarian maturation of the prawn Penaeus japonicus. The ovarian lipid concentrations increased during the slight mature and yellow ovarian periods, remained at roughly constant levels during the subsequent ovarian period to spawning, and then decreased to low levels at the spent ovaries. The hepatopancreatic lipid concentrations increased with increasing maturity of the ovaries, reached a maximum level at the yellow period of ovaries, and then decreased during the subsequent period to spawning. These results suggest the possible movement of hepatopancreatic lipids to the ovaries during the ovarian maturation. Both triglycerides and phospholipids were responsible for the increase in ovarian lipid concentrations during the sexual maturation. The fatty acid composition of lipids, trigly-cerides, and phospholipids of the ovaries did not vary markedly during the ovarian maturation.