Abstract: Objective To investigate the role of AGGF1 in DNA damage repair and modulating chemotherapy resistance in human colon cancer cells. Methods Cisplatin-induced human colon cancer HCT116 cells transfected with AGGF1 siRNA and siNC via Lipofectamine 2000 were examined for AGGF1, γH2AX and pNBS1 expressions using Western blotting. Immunofluorescence analysis was used to detect the recruitment of phosphorylated γH2AX and AGGF1 at the site of cisplatin-induced double-strand DNA breaks, and MTS method was used to investigate the proliferation of the damaged cells. Immunohistochemical method was used to detect the expression level of AGGF1 in human colon cancer and adjacent normal tissues. Results Western blotting showed that AGGF1 expression was significantly down-regulated in HCT116 cells after cisplatin exposure, and transfection withAGGF1 siRNAobviously inhibited the expression of phosphorylated γH2AX and NBS1. Immunofluorescence assay showed the co-localization of AGGF1 and γH2AX. Down-regulation of AGGF1 mediated by siRNA obviously increased the chemosensitivity of the cells (P<0.01). In the clinical specimens, AGGF1 was found to be overexpressed in colon cancer tissues as compared with the adjacent normal tissues (P<0.01), suggesting its association with the malignant phenotype of the tumor. Conclusion Down-regulation of AGGF1 inhibits DNA damage repair and increases the chemosensitivity in colon cancer cells possibly in relation with the suppressed phosphorylation of NBS1.