Reactive oxygen species (ROS) play crucial roles in maintaining redox balance and regulating physiological processes, ROS levels in cancer cells are relatively higher than those in normal cells. Therefore, elevating cellular ROS levels may be a viable strategy for selective killing of cancer cells. In this work, we synthesized a series of new theobromine derivatives and evaluated their cytotoxicity against gastric cancer cells MGC-803, SGC-7901 and HGC-27. Particularly, MQS-14 potently inhibited cell growth of MGC-803, SGC-7901 and HGC-27 cells at low micromolar levels. Mechanistic studies showed that compound MQS-14 decreased cell viability of MGC-803 cells and inhibited cell division revealed by the CFDA and EdU staining assays. MQS-14 increased cellular ROS levels and activated the MAPK pathway accompanied by the decreased p-ERK and increased p-JNK expression. MQS-14 also induced DNA damage and apoptosis in MGC-803 cells. To conclude, MQS-14 induced cell death of MGC-803 cells partly through elevating cellular ROS levels.