〔Abstract〕 Objective To investigate the effects of usnic acid(UA) on proliferation, cell cycle, apoptosis and autophagy of lung cancer cells A549 and NCI-H358. Methods The CCK-8 method was used to detect the inhibitory effect of UA on two kinds of lung cancer cells proliferation. Flow cytometry was used to detect the cell cycle arrest effect of UA on two types of lung cancer cells. The fluorescence amount of UA-induced reactive oxygen species(ROS) in two kinds of lung cancer cells were detected by DCFH-DA probe assay and flow cytometry. Western blot was used to detect the expression of apoptosis related proteins Bax, Caspase-3, Cleaved-Caspase-3, and autophagy related proteins LC3-Ⅰ and LC3-Ⅱ in two types of lung cancer cells after treatment with UA and UA+ROS inhibition. Results(1) Usnic acid reduced the survival rates of two types of cells and had a stronger ability to inhibit the proliferation of A549 cells than NCI-H358 cells.(2) Usnic acid blocked A549 cells in the G0/G1phase, while NCI-H358 cells in the G2/M and S phases.(3) Usnic acid induced an increase in ROS content in two types of cells. Compared to A549, NCI-H358 cells showed a greater increase in ROS, and the ROS inhibitor reduced the intracellular ROS increase induced by UA.(4) Usnic acid induced high expression of apoptosis-related proteins Bax and Cleaved Caspase-3 and increased the ratio of autophagy-related proteins LC3-Ⅱ/LC3-Ⅰ in both lung adenocarcinoma cells, and its pro-apoptotic and autophagic effects were stronger in A549 than in NCI-H358. After ROS inhibition, the expression levels of Bax and Cleaved Caspase-3 and the LC3-Ⅱ/LC3-Ⅰ ratio of both lung adenocarcinoma cells decreased, and the decrease was greater in NCI-H358 cells. Conclusion Usnic acid inhibits the proliferation of lung cancer A549 and NCI-H358 cells, induces cell cycle arrest, and induces apoptosis and autophagy in cancer cells. The inhibitory and killing effect of UA on A549 cells is stronger than that on NCI-H358 cells. In this case, the induced cell ROS are involved in the action of UA in two types of lung cancer cells. In contrast to A549 cells,ROS might play a more significant role in mediating the apoptosis and autophagy induced by usnic acid in NCI-H358 cells.