Growth hormone (GH) is obligatory for growth and development. But, there is controversy on the GH effect about reproductive processes of sexual differentiation, pubertal maturation, gonadal steroidogenesis, gametogenesis and ovulation. This study was conducted to investigate the effect of GH on estrus, ovulation and embryo implantation. The results obtained were as follows. GH stimulated to increase estrus rate (p<0.05), pregnancy rate (p<0.05), and total fetus number in mice treated for superovulation. Also, the correlation between GH and steroids, E2 and P4, at peri-estrus stage/ peri-ovulation stage/ peri-implantation stage of the superovulation-induced mice was examined. Consequently, GH co-injected with PMSG especially increased P4 level (p<0.05) at peri-estrus stage of superovulationinduced mice. In conclusion, GH co-treatment in superovulation system boosted the rate of estrus, pregnancy and total fetus by increasing progesterone level at peri-estrus stage of superovulation-induced mice.