OBJECTIVE: Granulocyte-macrophage colony stimulating factors known to be secreted in murine and human reproductive tract. The development of human, bovine and murine embryos could be promoted by addition of GM-CSF in culture medium. However, the pregnancy and implantation rate of embryos cultured in GM-CSF have not been evaluated. The aim of this study was to assess the effect of GM-CSF in embryo development, pregnancy and implantation rate. METHODS: A total of 191 IVF cycles were divided into control and GM-CSF supplement group (control =96, GM-CSF=95). The embryos were cultured for three day with or without 2 ng/ml of recombinant human GM-CSF. The quality of embryo, developmental velocity, pregnancy and implantation rates were compared. RESULTS: There was no difference in age, number of gonadotropin ampules used, number of oocytes and fertilization. The number of ICSI cycle was higher in GM-CSF group. In GM-CSF group, G-1 grade embryos were the highest in proportion (56.4%), while G-2 grade embryos were highest (44.3%) in control group. The developmental velocity of embryos were not different between GM-CSF and control group. The pregnancy and implantation rates were significantly higher in GM-CSF group than control (47.4% vs. 33.3%, 17.0% vs. 11.1% respectively). CONCLUSION: By adding GM-CSF in culture medium, the quality of embryo, pregnancy and implantation rate could be improved.