Objective To explore the molecular mechanism of inhibiting the proliferation of colorectal cancer cell HCT116 by curcumin. Methods The HCT116 cells were cultured in vitro and assigned to the control group, EGF group (using 20 ng/mL EGF alone) and EGF+curcumin groups. The effects of different concentrations of curcumin (0, 10, 20, 50, 100, and 200 μmol/L) on the proliferation rate of HCT116 cells were detected with MTT assay. The inhibiting effect of curcumin on the proliferation of HCT116 cells was detected with cell anchoring proliferation assay. The effects of curcumin on the activity of phosphorylase b kinase (PBK) were detected with in vitro kinase assay and beads binding assay. The effects of curcumin on the downstream signal pathways of PBK were detected by Western blotting and immunohistochemistry. Results Curcumin at a concentration <50 μmol/L had small effect on HCT116 cells, while the apoptosis of HCT116 cells increased significantly when the concentration of curcumin reached 100 μmol/L. The results of cell anchoring proliferation assay for HCT116 cells in soft agar showed that the size and number of clones of HCT116 cells in the EGF+curcumin groups decreased in a concentration dependent manner as compared with the EGF group. The in vitro kinase assay and beads binding assay suggested that curcumin could bind with PBK and inhibit the activity of PBK. Results of Western blotting and immunohistochemistry indicated that curcumin significantly down-regulated the phosphorylation of PBK downstream signal molecules ERK1/2 and H3 in a concentration and time dependent manner. Conclusion Curcumin has anti-proliferation effect on colorectal cancer cell HCT116 via inhibiting the activity of PBK.