Abstract: ObjectiveTo analyze vitamin D 1,25-dihydroxyvitamin D3(1,25(OH)2D3) and carboplatin(CBP) either drug alone and combined anti-tumor,effects on human lung cancer A549 cells,and to explore the possible mechanism of action. Methods The cells were divided to 1,25(OH)2D3 group,CBP group and combined treatment group.Cell viability was determined by CCK-8;expression of VDR was measured by immunofluorescence.The distributions of cell cycle,reactive oxidative species(ROS)and mitochondrial membrane potential(MMP)were analyzed by flow cytometry. Results Our results showed that although each of the drugs alone displayed antiproliferative activity,the growth inhibition of A549 cells was significantly enhanced in the combination group.Meanwhile,higher VDR expression was detected in A549 cells.Flow cytometry analysis indicated that the distribution of G₀/G₁ phase cells in combined group was remarkably increased,whereas,S phase and G2/M phase cells were significantly decreased.The trend is more evident in combination group.The content of ROS in combined group was significantly higher meanwhile MMP was lower than those in the alone drug group. Conclusion 1,25(OH)2D3 not only was able to suppress growth of A549 cells,but also enhance the anti-proliferative effect of CBP by inducing cell cycle arrest,increasing ROS and reducing MMP.