ABSTRACT. We investigated the effects of BCL2 transfection on the cell cycle and proliferation of GES-1 cells. A pcDNA3-BCL2 plasmid was used to transfect GES-1 cell line human gastric epithelial cells. Clones were obtained by G418 screening. BCL2-positive cells were identified by fluorescence immunohistochemistry. The pcDNA3-BCL2 vectors carrying the NeoR gene were transfected into GES-1 cells, while the empty plasmid was transfected into the same cells as controls. cytometry was used to detect the cell cycle. Hematoxylin and eosin (H&E) staining revealed morphological changes, and the effects of BCL2 transfection on cell proliferation were analyzed by cell counting and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The plasmid pcDNA3-BCL2 was identified by restriction enzyme digestion. Different degrees of BCL2 gene expression were detected in all seven clones. BCL2 was expressed mainly in the cytoplasm and the nuclear membrane. There were significantly more S-phase cells in the transfection group than in the controls. The morphology did not change after H&E staining. Cell growth was faster than in the controls after transfection for 6 days. At 24, 48, and 72 h after transfection, the A values were 4.15 ± 0.31, 5.98 ± 0.56, and 8.94 ± 0.79; those of the controls were 3.01 ± 0.20, 4.76 ± 0.52, and 7.69 ± 0.84; there was a significant difference between the two groups (P < 0.05). BCL2 transfection increased GES-1 cells in the S phase; the GES-1 cells were stable and BCL2 expression was high, which promoted cell proliferation. BCL2-positive clones were screened by neomycin 418 (G418). Flow