Pharmacological inhibition of DNA repair pathways has been emerging as an effective tool for cancer treatment. Poly(ADP-ribose) polymerase (PARP) is involved in DNA repair and transcriptional regulation and is now recognized as a key regulator of cell survival and cell death. In vitro and in vivo data suggest that PARP inhibitors could be used not only as chemo/radiotherapy sensitizers but also as single agents to selectively kill cancer cells in certain types of tumors. In the present study, we investigate the effects of 3-aminobenzamide (3-AB), a potent inhibitor of PARP, on human osteosarcoma cells and whether or not it can sensitize the tumor cells to chemotherapeutic agents. The results indicated that 3-AB suppressed U2OS cell growth in a time- and dose-dependent manner, and the suppressive effects of 3-AB were associated with increased cell apoptosis. In addition, 3-AB suppressed cell invasion in vitro and enhanced the suppressive effects of cisplatin in U2OS cells. Our work suggests that this PARP-I inhibitor may be developed into an effective agent for the treatment of human osteosarcoma.