Objective To investigate the sensitization effect of Ailanthone (AIL) on cisplatin-resistant A549/DDP cells of non-small cell lung cancer. Methods The effects of AIL on the viability of A549 and A549/DDP cells were detected by MTT. Analysis of the combined drug use index(CI) of Ailanone and cisplatin using Chou-Talalay. Cell cycle and apoptosis were detected by flow cytometry, and the expression of apoptosis-related proteins were detected by Western blotting. Results AIL (0.6μmol/L) and DDP (50μg/mL) had synergistic effect. Cell cycle arrest and apoptosis rate increased in G1 phase. The protein expression of caspase-3 and bcl-2 decreased, but the protein expression of Cleaved Caspase3, Bax, CDK4 and CyclinD1 increased. Conclusion AIL enhanced the sensitivity of DDP to A549/DDP, and increased the growth inhibition and apoptosis of DDP on A549/DDP.