Objective: To investigate the inhibitory effect of the combined treatment with oxaliplatin (LOHP) and low molecular weight citrus pectin (LCP) on the proliferation of human colon cancer cell line HCT116 and its mechanism. Methods: The effect of LOHP alone and LOHP combined with LCP on the proliferation of HCT116 cells was determined by MTT assay. The apoptosis rate and cell cycle of HCT116 cells after the above two treatments were detected by Flow cytometry (FACS), and the changes of procaspase-3, -8, -9 and poly (ADP-ribose) polymerase (PARP) of the cells after treatments were analyzed by Western blot. Results: Both treatments had inhibitory effect on the proliferation of HCT116 cells, and the combination of LOHP and LCP exerted stronger inhibitory effect than LOHP alone treatment (P＜0.05). FACS analysis showed that both treatments increased the apoptosis rate of HCT116 cells, and the apoptosis rate of the combined treatment was significantly higher than that of the LOHP alone treatment (P＜0.01). Both treatments decreased the G0/G1 phase and increased G2/M phase of the cells, while the G2/M phase ratio of the combined treatment was increased more significantly higher than that of the LOHP alone treatment (P＜0.05). The expressions of procaspase-3, -9, and PARP protein were all down-regulated after both treatments, and those down-regulations after the combined treatment were more obvious compared with those after LOHP alone treatment. The expression of procaspase-8 showed no obvious difference after the two treatments. Conclusions: LCP can increase the inhibitory effect of LOHP on proliferation of human colonic cancer cell line HCT116, and this effect may be related to modulation of the cell cycle and activation of mitochondria aboptosis pathway.