The present study assessed the antitumor effect of artesunate (ART) in?vitro and in?vivo, as well as its underlying mechanism of action in HCT116 colon cancer cells. An MTT assay, DAPI staining, flow cytometry, western blotting, immunohistochemistry, transmission electron microscopy and TUNEL assay were performed to study the molecular mechanism underlying the antitumor effects of ART in HCT116 colon cancer cells. ART was observed to inhibit proliferation by inducing the apoptosis of HCT116 cells both in?vitro and in?vivo. Flow cytometry analysis demonstrated that treatment with 2 and 4??g/ml ART for 48?h induced early apoptosis in 22.7 and 33.8% of cells, respectively. In the xenograft tumors of BALB/c nude mice, TUNEL?positive cells increased in the ART group compared with that in the normal saline group. Furthermore,the associated mitochondrial cleaved?caspase 3, poly?ADP ribose polymerase (PARP), caspase 9 and Bcl?2?associated X protein levels increased while B?cell lymphoma?2 (Bcl?2) decreased both in the cell and animal ART?treated group. ART?treated cells also exhibited autophagy induction, as evidenced by increased protein expression levels of light chain 3 (LC3) and beclin?1, and the presence of autophagosomes. Notably, pharmacological blockade of autophagy activation using hydroxychloroquine markedly enhanced ART?induced apoptosis and increased the protein levels of cleaved caspase 3 and PARP, while decreasing the levels of LC3 and beclin?1. These findings suggested that the ART?induced autophagy may have a cytoprotective effect by suppressing apoptosis. In conclusion, ART may be a potentially clinically useful anticancer drug for human colon cancer. In addition, co?treatment with ART and an autophagy inhibitor may be an effective anticancer therapy.