Objective To explore the effects of over-expression high-mobility-group A2(HMGA2) on proliferation and cell cycle in primary cultured human growth hormone-secreting pituitary tumor cells .Methods The protein expression of HMGA2 in growth hormone-secreting pituitary tumor cells transfected by HMGA2 overexpression plasmid (transfection group) were detected by Western blot .The effects of the HMGA2 overexpression on cell proliferation ,cell cycle were measured by (cell counting kit-8 , CCK-8) assay and flow cytometry respectively .Results HMGA2 protein of transfection group was higher than the blank load transfection group(tranfectied with pcDNA3 .1 plasmid) after 24 h (P<0 .05) .To compare with the blank load transfection group , cells overexpression of HMGA2 could drastically increase the ability of proliferation at 24 ,48 ,72 ,96 h and increase the S phase rati-o of cell cycle and decrease the G1 phase ratio of cell cycle ,the difference was statistically significant (P<0 .05) .Conclusion Over-expression of HMGA2 increases pituitary tumor cells proliferation ability and promote cells G 1 phase progress .