WYK431, a novel synthetic quinazoline derivative, showing potent inhibition of proliferation activity against a broad spectrum of human cancer cell lines. We investigated the anticancer effects of WYK431 on BGC823 cells both in vitro and in vivo. The results showed that WYK431 inhibited proliferation, arrested the cell cycle at the G(2)/M phase, which was related to CDK1 and CDC25C, and induced apoptosis associated with activation of caspase-3 and caspase-9 rather than caspase-8 in BGC823 cells. Treatment of BGC823 cells with WYK431 resulted in upregulation of Bax, release of cytochrome c from the mitochondria to the cytosol and disruption of mitochondrial membrane potential. Western blot analysis showed that WYK431 downregulated the levels of the PI3K/Akt signaling pathway. Moreover, WYK431 effectively suppressed tumor growth in xenograft models in BALB/c athymic nude mice without major side action. TUNEL analysis showed that WYK431 induced BGC823 cell apoptosis in vivo. Collectively, WYK431 is a novel small molecule agent which inhibits BGC823 cell proliferation inducing G(2)/M phase arrest and apoptosis via the mitochondrial apoptotic pathway. To assess its potential as a promising anticancer agent requires further investigation.