The luminal fluid environment of the female reproductive tract is considered critical for the sperm to undergo a series of molecular events leading to the final acquisition of their fertilizing capacity. It has been shown that the fluid in the female reproductive tract contains high content of HCO3- and it plays an important role in sperm functions including sperm motility, capacitation, hyperactivation and acrosome reaction. This review summarizes the effects of HCO3- on sperm functions occurring in the female reproductive tract and discusses the transport mechanisms involved in mediating uterine HCO3- secretion. New evidence is also presented to show possible cause of female infertility due to defective HCO3- transporting mechanism.