BACKGROUND Recent researches discovered that artemisinin and its derivatives had anti-tumor activity. Dihydroartemisinin is one of the derivatives with higher activity. This study is to explore the effect of dihydroartemisinin on the proliferation of human lung adenocarcinoma cell line A549, so as to provide experimental base for treatment of lung cancer. METHODS Inhibition of proliferation in vitro was measured by MTT assay. The cell growth curve was drawn according to cell counts. The population doubling time was counted in logarithmic growth phase, DNA contents were measured by flow cytometry. Cell cycles were observed at the same time after the treatment. And the nude mice bearing A549 cancer cells were applied to detect the effect of dihydroartemisinin in vivo. RESULTS Dihydroartemisinin inhibited A549 cell proliferation in a concentration-dependent manner, after 96h of treatment, the IC50 for dihydroartemisinin inhibition of cell number was 0.23μmol/l. The population doubling time for human lung adenocarcinma in the control group was 21.3h and that in the dihydroartemisinin group was 38.5h . An highly significant difference was observed between the two groups (P < 0.01). Cells in G0 plus G1 were increased after the dihydroartemisinin treatment. The tumor inhibiting rate of dihydroartemisinin was 54.3% in vivo. CONCLUSIONS Dihydroartemisinin has marked anticancer activity on human lung adenocarcinoma cell line A549 both in vitro and in vivo. The inhibition in vitro is related to blockade of G0 and G1 phases.