Autophagy has become a promising target for cancer therapy. Fangchinoline (Fan) has been shown to exert anticancer effects in some types of cancers. However, the anticancer effects on colorectal cancer (CRC) and the underlying mechanisms have never been elucidated. More specifically, regulation of autophagy in CRC by Fan has never been reported before. In the present study, Fan was found to induce apoptosis and autophagic flux in the CRC cell lines HT29 and HCT116, which was reflected by the enhanced levels of LC3-II protein and p62 degradation, and the increased formation of autophagosomes and puncta formation by LC3-II. Meanwhile, combination with the early-stage autophagy inhibitor 3-methyladenine (3-MA) but not the late-stage autophagy inhibitor chloroquine (CQ) further increased Fan-induced cell death, which suggested the cytoprotective function of autophagy induced by Fan in both HT29 and HCT116 cells. Moreover, Fan treatment demonstrated a dose- and time-dependently increase in the phosphorylation of AMPK and decrease in the phosphorylation of mammalian target of rapamycin (mTOR) and ULK1, leading to the activation of the AMPK/mTOR/ULK1 signaling pathway. Furthermore, in the HT29 xenograft model, Fan inhibited tumor growth in vivo. These results indicate that Fan inhibited CRC cell growth both in vitro and in vivo and revealed a new molecular mechanism involved in the anticancer effect of Fan on CRC, suggesting that Fan is a potent autophagy inducer and might be a promising anticancer agent. CI - Copyright (c) 2021 The Authors. Published by Elsevier Inc. All rights reserved.