Abstract: The experiment was carried out to study the effects of in vitro culture systems on the bovine embryo's sex ratio. The results indicated that the sex ratio of male blastocysts versus female blastocysts was different from the expected 1∶1 ratio but no significant different (P>0.05) in the two culture systems supplemented with FCS. While the total sex ratio of blastocysts derived from all kinds of culture systems was different from the 1∶1 ratio significantly (P<0.05). It demonstrated that the capacity developing to the blastocyst stage of male embryos were stronger than that of female embryos in vitro culture system, and the presence of serum has a beneficial effect on the development of male embryos.