Gastric cancer (GC) is one of the most common malignancies and has the second highest lethal rate in the world; thus, finding new medicines with high potency and low toxicity is urgent. Cudrania tricuspidata (Carr.) Bur. ex Lavallee (Moraceae) is a traditional medicinal herb that is considered to have antitumour efficacy. We extracted and isolated cudraxanthone L (CXL) from Cudrania tricuspidata and evaluated its anti-cancer efficacy. CXL treatment inhibited angiogenesis of chorioallantoic membrane (CAM) and repressed the cell viability of various human cancer cells, indicating it presented the antitumour potential. Among them, CXL presented the best inhibitory effects on MGC803 cells. In addition, the invasion, migration and clonogenicity were significantly repressed, S phase of the cell cycle was arrested, and apoptosis was induced when MGC803 cells were treated with CXL. The results of RNA sequencing, qRT-PCR and western blotting verified that CXL regulated the MAPK signalling pathway and induced apoptosis by FAS-mediated pathway. The in vivo data revealed that CXL arrested tumour growth without toxic effects and upregulated the protein levels in FAS-mediated pathway in MGC803 gastric cancer-bearing mice. In summary, we demonstrate CXL presents impactful anti-GC efficacy by regulating the MAPK signalling pathway and promoting the FAS-mediated pathway.