Abstract: Objective To investigate the effect of radiosensitization of Poly (ADP-Ribose) polymerase inhibitor-Veliparib on Ishikawa cells, and to explore its potential mechanism. Methods Human endometrial carcinoma Ishikawa cells cultured in vitro were divided into four groups: Control group, Veliparib group, Radiotherapy group (RT), Veliparib combined with RT group. Cell Counting Kit-8 (CCK-8) assay was used to analyze the 10% inhibitory concentration (IC10) and 50% inhibitory concentration (IC50) of Veliparib to Ishikawa cells. The radiosensitization effect of Veliparib on Ishikawa cells was evaluated by clonogenic assay. The expression of γH2AX (DNA injury-associated protein) was observed by Western blot in vitro. Results The IC10 and IC50 value of Veliparib were 1.4 μmol/L and 130.1 μmol/L. The radio-sensitivity enhancement ratio (SER) of Veliparib combined with RT was 1.413 in vitro. Western blot results confirmed that the expression levels of γH2AX was significantly higher in the Veliparib+RT group (P<0.05). Conclusion Our in vitro data demonstrated decreased in the radiobiological effects on Ishikawa cells after addition of Veliparib to radiotherapy, which can be explained by less DNA repair, increased DNA double strand break and induction of cell apoptosis.