en Original Article Original Article - The cytokine of granulocyte macrophage colony stimulating factor (GM-CSF) is a glycoprotein, which is synthesized in the female reproductive tract and has embryonic trophic effect in mammals. The objective of this study was to examine the optimal dosage of GM-CSF to improve the mouse embryo development in vitro. To collect two and eight cells embryos, the pregnant NMRI mice were sacrificed by cervical dislocation at 48 h and 72 h post hCG injections, respectively. The embryos were cultured randomlly in T6 medium supplemented with 5 mg /ml bovine serum albumin (BSA) and 0, 2, and 10 ng / ml human rGM-CSF. The data of blastocyst formation and hatching in different groups of embryo culture were compared by chi-square analysis. The results showed that the developmental rates of 2 and 8 cells embryos to hatching blastocyst in the presence of 2 ng/ml of GM-CSF their control groups (51.5% and 49.7%, respectively) were more than those in the other groups, but insignificant. It seems more researches are necessary to confirm this suggestion that the GM-CSF with 2 ng/ml concentration may have a better potential, not only to enhance the developmental rates of 2 and 8 cells embryos but also for decreasing the degeneration of those embryos. Granulocyte Macrophage Colony Stimulating Factor, Embryo Development 12 14 http://ijrm.ir/browse.php?a_code=A-10-100-22&slc_lang=en&sid=1 Behnaz Sheikholslami Yes Mojdeh Salehnia No Mojtaba Rezazadeh No