Abstract: Objective To study the effect of Bcl2-siRNA on sensitivity of cisplatin-resistant human lung adenocarcinoma A549/DDP cells to cisplatin. Methods Forty-eight hours after Bcl2-siRNA was transfected with cisplatin-resistant human lung adenocarcinoma A549/DDP cells,a fresh cisplatin solution was prepared by adding different concentrations of cisplatin（0μg/ml,3μg/ml,6μg/ml,9μg/ml,12μg/ml,15μg/ml） into A549/DDP cells to measure their growth-inhibition rate by CCK-8 assay.Expression of Bcl-2 mRNA and protein in A549/DDP cells-transfected Bcl2-siRNA was detected by Real time RT-PCR and Western blot,respectively. Results The expression of Bcl-2 mRNA and protein in A549/DDP cells-transfected Bcl2-siRNA decreased 92.6%（P＜0.05） while the sensitivity of A549/DDP cells to cisplatin increased 57.8%（P＜0.05）. Conclusion Bcl2-siRNA can decrease the expression of Bcl-2 mRNA and protein in A549/DDP cells,and increase the sensitivity of A549/DDP cells to cisplatin.