Cannabinol (CBN) is a weak-psychoactive cannabinoid and has been shown to exert several bio-logical activities. At the same time, not much is known about the anti-cancer activities of CBN. In this report, we characterized the anti-tumor effects of CBN on the glioma A172, liver cancer HepG2 and breast cancer HCC1806 cell lines. We found that CBN reduces the proliferation of the analyzed cancer cells and modulates the level of cannabinoid receptors, including GPR18, CB2 and GPR55. Furthermore, CBN inhibits the ERK1/2 pathway in A172 and HepG2 cells, while suppressing the AKT pathway in HCC1086 cells. Moreover, CBN may cause apoptosis through downregulation of p21 and p27 as well as a cell cycle arrest at G1 or S-phase via decreasing the CDK1, CDK2, and cyclin E1 levels. Taken together, these results offer new insights into the anti-cancer properties of CBN.