OBJECTIVE Lysine-Specific Demethylase 1 (LSD1) inhibitors have been developed and reached the clinic, but its effect in combination with cytotoxic chemotherapy is unclear. Here, we investigated the anti-tumor effect of LSD1 inhibitor GSK-LSD1 and its anti-tumor effect with the DNA damage drug doxorubicin (DOX) in gastric cancer (GC) cells. METHODS Cells were treated with different concentrations of GSK-LSD1 to examine the anti-tumor effect versus cell viability by MTT and cell cycle arrest by flow cytometry. To explore whether LSD1 inhibitors can increase the anti-tumor effect of DNA damage drugs, cells were treated with DOX for 48 h after pretreatment with GSK-LSD1 for 48 h. Cell viability was detected by MTT and apoptosis-related proteins were examined by Western blot. Furthermore, anti-tumor efficacy of combination GSK-LSD1 with DOX was also measured in MGC-803 xenografts model in nude mice. RESULTS The results showed that LSD1 was highly expressed in GC cell lines. Inhibition of LSD1 has a weak effect on cell viability and cell cycle. Moreover, LSD1 inhibitors pretreatment could significantly increase the anti-tumor effect of DOX. Further study found that inhibition of LSD1 can significantly enhance DOX-induced the apoptosis, accompanied by down-regulation of antiapoptotic Bcl-2 expression and up-regulation of proapoptotic Bax expression. We also confirmed that inhibition of LSD1 can sensitize the anti-tumor effect of DOX in vivo. CONCLUSIONS Our findings suggest that the LSD1 inhibitor GSK-LSD1 has a weak inhibitory effect on the viability and cell cycle of GC cells, but can enhance the sensitivity of DOX.