Objective: To determine the effects of leukemia inhibitory factor (LIF) on embryonal development in in vitro culture. Methods: This is designed in vitro model using eggs from mouse. The eggs from mouse were assigned 29 for control group, 53 for 20 ng/ml of LIF, 88 for 40 ng/ml of LIF, 68 for 80 ng/ml of LIF respectively for in vitro fertilization. And 26 fertilized eggs at 2 cell stage from mouse also were assigned. The mouse embryos of all groups were cultured in medium supplemented with LIF in different concentrations, whereas the eggs in control group was cultured in medium without supplement of LIF. Results: At 72 hours culture of eggs from in vitro fertilization, there was a slight increas in rate of embryonal development to morula in both LIF-20 and LIF-40 as results of 64.15% and 75% respectively, while 42.65% in inferior rate of LIF-80, compare with 51.72% in control group. But the difference between these each groups were not significant in statistically ($p{le}0.05$). And after 96 hours culture of eggs, the rates blastocyst formation was significantly higher in both LIF-20 and LIF-40 as 56.6% and 63.63% than those in control and LIF-80 as 44.83% and 35.29% respectively. On culturing eggs from in vivo fertilization, the rates of blastocyst formation was significantly not only higher as 85% and 81.81% respectively in medium supplemented with LIF-40 and LIF-80 than 42.3% in LIF-20 but also embryonal cell viability were remakedly improved at 96 hours after culture. Conclusion: The LIF in low dose is embryotrophic, but LIF in high dose is embryotoxic on eggs from in vitro fertilization. Whereas on culturing eggs from in vivo fertilization, LIF is more beneficial with dose dependent in high concentration.