The PI3K pathway is aberrantly activated in many cancers and plays a critical role in tumour cell proliferation and survival, making it a rational therapeutic target. In the present study, the effects and the underlying mechanism of a new PI3K inhibitor, W941, were investigated in non-small-cell lung cancer (NSCLC). The results of this study showed that W941 inhibited the growth of A549 and Hcc827 cells with IC50 values of 0.12 and 0.23 μM, respectively, and that W941 markedly inhibited the growth of A549 xenograft tumours in a nude mouse model without decreasing body weight. Western blotting assays showed that W941 inhibited the phosphorylation of downstream proteins in the PI3K pathway (AKT, mTOR, p70S6K and 4EBP1) in both A549 and Hcc827 cells. In addition, after W941 treatment, a dose-dependent increase in the ratio of the LC3-II/I ratio was observed. When cells were pre-treated with chloroquine or bafilomycin A1, W941 increased the LC3-II/I ratio, suggesting that W941 acted as an autophagy inducer. Moreover, autophagy blockers enhanced apoptosis after W941 treatment, indicating that W941-induced autophagy actually protected the cells against its cytotoxicity. Our findings suggest that the combination of a PI3K inhibitor with an autophagy inhibitor might be a novel option for NSCLC treatment.