Objective: To elucidate the mechanism of melatonin combined with cisplatin in promoting cell apoptosis of rat pancreatic cancer AR42J cells. Methods: Rat pancreatic cancer AR42J cells were divided into control group, 1 mmol/L cisplatin treated group (cisplatin group), 1 mmol/L melatonin treated group (melatonin group), 1 mmol/L cisplatin combined with 1 mmol/L melatonin treated group (combined group), 1 μmol/L cisplatin combined with melatonin treated group after 1 μmol/L PBN pretreatment for an hour (PBN+ combined group) and 1 μmol/L cisplatin combined with melatonin treated group after PBN solvent pretreatment for an hour (solvent+ combined group). MTT and annexin V-FITC/PI were used to detect the cell proliferation rate and cell apoptosis rate, respectively. The protein expression of caspase-3 was detected by Western blot. DCFH-DA was used to detect the level of ROS. ROS level and caspase-3 expression in AR42J cells pretreated with ROS antagonist PBN for 24 hours were detected. Results: The cell proliferation rate of control group, cisplatin group, melatonin group and combination group after 24-hour culture was (96.29±3.49)%, (81.38±6.01)%, (80.72±3.68)% and (42.26±6.35)%, respectively. The cell apoptosis rate was (16.42±4.15)%, (56.47±9.06)%, (52.94±6.57)% and (87.36±6.48)%, respectively. The percentage of ROS positive cells was (1.33±1.53)%, (46.67±7.64)%, (45.67±5.13)% and (83.33±7.64)%, respectively. The expression of cspase-3 was 100%, (150.64±7.70)%, (147.00±7.27)% and (190.04±5.07)%, respectively. The cell proliferation rate of cisplatin group and melatonin group was significantly lower than that of the control group. The apoptotic rate, the proportion of ROS positive cells and the expression of caspase-3 were significantly higher than those in control group. The changes in the combined group were more obvious than those in the single drug treatment group, and the differences were all statistically significant (all Pvalues <0.05). The percentage of ROS positive AR42J cells [(45.24±4.64)% vs (84.90±6.13)%)] induced by melatonin combined with cisplatin could be significantly reversed by PBN pretreatment for 1 hour, and the expression of caspase-3 in AR42J cells could be down regulated (124.92±9.72 vs 184.69±7.76) with statistically significant difference (all P values<0.05). Conclusions Melatonin combined with cisplatin may promote cell apoptosis of pancreatic cancer AR42J cells through ROS/caspase-3 pathway.