Abstract: Objective : To study the effect of REGγ gene expression on the proliferation and apoptosis of humanbreast cancer MCF-7 cells. Methods : To construct the eukaryotic expression recombinant PcDNA3.1-REGγ,MCF-7 cells were transfected with PcDNA3.1-REGγ or the empty vector using lipofectamine 2000, and thestably transfected cells were selected after exposure to 800mg/L of G418 for 6 weeks. The effect of REGγgene expression on cell growth was examined by MTT assay. Immunocytochemistry was performed to detectthe differences in proliferative cell nuclear antigen (PCNA) in MCF-7 cells. Apoptosis was measured via flowcytometry, and caspase 3 expression was determined using spectrophotometry. Ultrastructural changes inMCF-7 cells were observed with transmission electron microscopy (TEM). Results : Western blot revealed thatthe expression of REGγ was highly increased in cells stably transfected with the recombinant vector com-pared with the control group (P<0.05). The doubling time of untransfected cells, cells transfected with emptyvector and cells transfected with recombinant vector was 34.6h, 35.1h, and 26.7h, respectively. The growthcurve indicated that cell growth was obviously accelerated in cells transfected with PcDNA3.1-REGγ. The lev-el of PCNA measured by immunocytochemistry in untransfected cells, cells transfected with empty vector andcells transfected with PcDNA3.1-REGγ was 89.61±14.32, 87.95±16.38, and 133.47±8.14, respectively. Theexpression of PCNA was remarkably higher in cells transfected with the REGγ gene (P<0.01). The optical den-sity (OD) was obviously lower in cells transfected with PcDNA3.1-REGγ (P<0.05), and the rate of apoptosiswas lower in cells transfected with PcDNA3.1-REGγ (P<0.01). Karyosome hypertrophy, mitochondrion abun-dance, Golgi apparatus abundance and ectasis were seen with TEM. Apoptotic bodies were not observed. Conclusion : The REGγ gene promotes cell proliferation and inhibits apoptosis in MCF-7 cells.