Combination chemotherapy regimen with several anti-tumor drugs is a strategy to improve outcome. Thymoquinone (TQ) has been reported to exert biological activity on various types of human cancers without obvious toxicity. However, only few studies showed the anti-tumor effects of TQ combination with cisplatin on gastric cancer (GC). Here, we showed pretreatment with 5μM TQ significantly increased the apoptotic effects induced by cisplatin on GC cell lines. Combined treatment of cisplatin with TQ represented a significantly superior tumor suppression effect than either agent alone in a xenograft tumor mouse model. Interestingly, TQ pretreatment following cisplatin caused a significant increase in the levels of PTEN, an obvious decrease in p-AKT, CyclinD1, P-glycoprotein (P-gp), meanwhile, TQ and cisplatin also led to an increase in Bax, Cyt C, AIF, cleaved caspase 9, and cleaved caspase 3, and a decrease in Bcl-2, procaspase-9, procaspase-3. Moreover, results , showed that a combination of TQ and cisplatin represents a more effective anti-tumor agent than either agent alone in a xenograft tumor mouse model. In conclusion, TQ significantly augments cisplatin-induced anti-tumor effects on gastric cancer both and , through inhibiting PI3K/AKT signaling pathway, activating the mitochondrial pathway, and down-regulating P-glycoprotein by up-regulating PTEN gene. TQ might be as a promising candidate as a cancer chemopreventive or chemotherapeutic agent for antineoplastic combination therapy and merits further clinical investigation.