We previously reported the potential of a novel small molecule (E)-methyl 3-(1-(4-methoxybenzyl)-2, 3-dioxoindolin-5-yl) acrylate (HKL 2-3-15) as an anticancer agent. This study was focused on the molecular mechanisms by which HKL 2-3-15 exerts its cytotoxic activity in human gastric cancer MGC-803 cells. We showed that HKL 2-3-15 induced G2/M phase arrest in a time-dependent and dose-dependent manner. Following the treatment, HKL 2-3-15 also caused Annexin-V staining, suggested HKL 2-3-15 caused apoptosis in MGC-803 cells. Collectively, our findings demonstrate that HKL 2-3-15, a 5-(2-Carboxyethenyl) isatin derivative, notably inhibits MGC-803 cell proliferation through the induction of G2/M cell cycle arrest and apoptosis. Its potential as a candidate anticancer agent warrants further investigation.