〔Abstract〕 Abstract Objective To investigate the effects of usnic acid(UA) on proliferation , cell cycle , apoptosis and au- tophagy 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 inhibi- tion . Result 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 /G1 phase , 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 intracel- lular 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 adenocarcino- ma cells , and its pro-apoptotic and autophagic effects were stronger in A549 than in NCI-H358 . After ROS inhibi- tion , the expression levels of Bax and Cleaved Caspase-3 and the LC3-Ⅱ/LC3 - Ⅰ ratio of both lung adenocarcino- ma cells decreased , and the decrease was greater in NCI-H358 cells . Conclusion Usnic acid inhibits the prolifer- ation 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 .