Hypoxia-inducible factor 1α (HIF1α) has been demonstrated to be involved in the resistance of various human cancer cells to chemotherapies. However, correlation between HIF1α and sensitivity of human non-small cell lung cancer (NSCLC) cells to cisplatin has not been illuminated. The aim of present study was to investigate the effects of HIF1α on drug resistance in NSCLC cells. A549 cells were incubated in 21% or 0.5% O 2 followed by the assessment of HIF1α level with qRT-PCR and western blot, and ROS levels by DCFH-DA assays. Effects of hypoxia or HIF1α inhibitor LW6 on the proliferation and apoptosis of A549 cells were evaluated via CCK-8 and flow cytometry assays. IC 50 of A549 cells to cisplatin was determined by MTT assay. The mitochondrial membrane potential (MMP) was measured via JC-1 staining. Moreover, the expression of apoptosis related protein (Bcl-2, Bax) and drug resistance related proteins (MDR1, MRP1) were measured by western blotting. Exposure of A549 cells to 1% O 2 significantly upregulated HIF1α expression, maintained cell viability to cisplatin but decreased the ROS level, which promoted chemoresistance to cisplatin. LW6-treated A549 cells showed an increase in ROS level that blocked the hypoxia induced resistance to cisplatin and in addition, decreased expression of MDR1 and MRP1 in cisplatin-treated cells. This study revealed that hypoxia-improved cisplatin chemoresistance of NSCLC cells by regulated MDR1 and MRP1 expression via HIF1α/ROS pathway is reversed by LW6, suggesting that LW6 may act as effective sensitizer in chemotherapy for NSCLC.