Abstract: Objective To investigate the effect of cyclin E expression on cells growth and cell cycle changes of human breast cancer MCF 7 cell line. Methods The recombination eukryotic expression plasmid of cyclin E was constructed, and transferred into the MCF 7 cell line with lipofectAMINE.Cell clones were selected with G418.Cells growth properties, 3H TdR and cell cycle analysis were done. Results The cyclin E overexpression could obviously increase the cells growth speed (1 52 fold higher than vector control) and DNA synthesis (1 75 fold) and also increase the cells progression from G1 to S phase.The hyperphosphorylation form of pRB was increased (3 fold). Conclusion High expression of cyclin E could effect the cell growth and cell proliferation probably through regulating the phosphorylation of pRB and G1 S progression.