The objective of this study was to examine the effect of bovine follicular fluid added to the matura-tion medium on sperm penetration, male pronucleus formation and polyspermy in pig oocytes fertilizedin vitro. Pig oocytes were cultured in 10 µl droplets of medium without bovine follicular fluid for 24 h.The oocytes were then cultured in 100 µl droplets of medium supplemented with 0,10 or 20% bovinefollicular fluid for further 24 h. The cultured oocytes were inseminated with boar sperm at a concentra-tion of 1×105or 106sperm/ml. When oocytes were inseminated at 1×105sperm/ml, significantly lowerproportion of penetrated oocytes was found in 20% bovine follicular fluid group compared with that in 0and 10% bovine follicular fluid groups (P<0.05). Addition of bovine follicular fluid to maturation medi-um promoted the male pronucleus formation in oocytes inseminated with 1×105sperm/ml, with a sig-nificant (P<0.05) difference in rate of oocytes with male pronuclei between 0 0x1.de8c8p-891nd 10% bovine follicu-lar fluid groups. Treatment with bovine follicular fluid during the second 24 h culture significantlydecreased the proportions of polyspermic oocytes inseminated with either of sperm concentrations.These results indicate that the presence of bovine follicular fluid in maturation medium enhances malepronucleaus formation and reduces polyspermic penetration in pig oocytes fertilized in vitro.