〔Abstract〕 Objective To investigate the effects of microRNA-29a(miR-29a) in mediating the regulation of dihydroartemisinin(DHA) on the immune checkpoint molecule B7H3 in lung adenocarcinoma(LUAD). Methods The expression level and prognostic significance of B7H3 in LUAD were analyzed by public database. Small interfering RNA(siRNA) was used to knock down B7H3 in LUAD cell lines A549 and HCC827, and cell proliferation was detected by CCK-8 method. A549 and HCC827 cells were treated with gradient concentrations of DHA(0, 5, 10, 25, 50, 100 μmol/L) for 48 h, and the half maximal inhibitory concentrate(IC50) was calculated. A549 and HCC827 cells were treated with IC50concentration of DHA for 1, 2 and 3 days, and the cell proliferation was detected by CCK-8 method. A549 and HCC827 cells were transfected with miR-29a inhibitor. After DHA treatment, the expression level of miR-29a was detected by RT-qPCR, and the expression level of B7H3 was detected by Western blot. Results B7H3 was overexpressed in LUAD and associated with poor prognosis. After knocking down of B7H3, the proliferation ability of A549 and HCC827 cells significantly decreased(allP<0.001). DHA inhibited the proliferation of A549 and HCC827 cells in both dose-and time-dependent manners, with IC50values of 30.16 μmol/L and 7.50 μmol/L, respectively. DHA up-regulated the expression of miR-29a in A549 and HCC827 cells(P<0.001,P<0.01), and down-regulated the expression of B7H3 in both cell lines(P<0.01,P<0.001). After transfection of miR-29a inhibitor into A549 and HCC827 cells, the expression of B7H3 was up-regulated, and the down-regulation of B7H3 by DHA was partially reversed. Conclusion miR-29a mediates the molecular regulation of DHA on B7H3 in LUAD.