Ailanthone is a major quassinoid extracted from the Chinese medicinal herb Ailanthus altissima, which has been reported to exert antiproliferative effects on various cancer cells. The present study aimed to investigate the antitumor effects of ailanthone on SGC‑7901 cells, and to analyze its underlying molecular mechanisms. Following treatment with ailanthone, Cell Counting kit‑8 was used to detect the cytotoxic effects of ailanthone on SGC‑7901 cells in vitro. The typical apoptotic morphology of SGC‑7901 cells was observed by Hoechst 33258 staining. Cell cycle progression and apoptosis were measured by flow cytometry, and the protein and mRNA expression levels of Bcl‑2 and Bax were analyzed by western blot analysis and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) respectively, in SGC‑7901 cells. The results of the present study indicated that ailanthone inhibited the proliferation of SGC‑7901 cells in a dose‑ and time‑dependent manner in vitro, and also demonstrated that ailanthone induced G2/M phase cell cycle arrest and apoptosis of SGC‑7901 cells. Furthermore, analysis of the underlying molecular mechanisms revealed that ailanthone downregulated the expression levels of Bcl‑2, whereas the expression levels of Bax were upregulated at the protein and mRNA levels. In conclusion, ailanthone may inhibit the proliferation of SGC‑7901 cells by inducing G2/M phase cell cycle arrest and apoptosis via altering the protein and mRNA expression levels of Bcl‑2 and Bax in SGC‑7901 cells.