Objective To inhibit NO production in embryonic cells using NO synthase(NOS) inhibitor L-NAME and to explore the regulatory function of NO as an important cellular messenger molecule in early embryonic development in vitro.Methods The embryos were produced by in vitro fertilization and then cultured in the embryonic culture medium including different concentrations of NOS inhibitor L-NAME.The cleavage rate of embryos on day 2 of culture,and the blastocyst rate and blastocyst total cell number on day 4 of culture were evaluated.Results The effect of 0.1 mmol/L L-NAME on the embryonic cleavage rate and blastocyst rate was not significant,but the total cell number of blastocysts was significantly decreased with increasing concentrations of L-NAME.One and 10 mmol/L L-NAME significantly reduced the embryonic cleavage rate,blastocyst rate and blastocyst total cell number.Conclusion NO plays an important regulatory role in the early embryonic development.The inhibition of NO production in embryonic cells has much effect on the early embryo development and their quality.