Polyunsaturated fatty acids ( PUFAs )play an important role in sperm quality and fertility.This study was conducted to investigate the effect of dietary supplementation with PUFAs on male mice reproductive capacity.Mice were fed a diet of 4％ soybean oil (SO),4％ fish oil (FO),or 4％ conjugated linoleic acid (CLA) for 30 days.Litter sizes and sperm quality were measured during the study.Litter size decreased in females mated with FO group males.Although sperm total number,motility,and in virto fertilization did not differ among treatments,the proportion of intact sperm membrane decreased in the FO group compared to other groups.This was supported by the increased proportion of damaged sperm membrane in the FO group.Furthermore,the percentage of high mitochonddal membrane potential (MMP) declined,but the percentage of low MMP was increased by dietary FO and CLA supplementation compared to the SO group.Sperm membrane phospholipid in mice receiving the FO diet had a higher concentration of docosapentenoic acid ( C22 ∶5n-3,DPA ),docosahexaneoic acid ( C22 ∶ 6n-3,DHA),and n-3 PUFAs,but lower levels of arachidonic acid ( C20∶4n-6,AA) and n-6 PUFAs compared to those receiving the SO diet.These data suggest that decreased sperm quality in mice fed a FO diet may be due to excessive DPA and DHA in the membrane.