In this study, two Pt(II) and three Pt(IV) complexes with the structures of [PtL2 Cl-2] (1), [PtL2 I-2] (2), [PtL2 Cl-2 (OH)(2)] (3), [PtL2Cl2 (OCOCH3)(2)] (4), and [PtL2Cl4] (5) (L = benzimidazole as carrier ligand) were synthesized and evaluated for their in vitro antiproliferative activities against the human MCF-7, HeLa, and HEp-2 cancer cell lines. The influence of compounds 1-5 on the tertiary structure of DNA was determined by their ability to modify the electrophoretic mobility of the form I and II bands of pBR322 plasmid DNA. The inhibition of BamH1 restriction enzyme activity of compounds 1-5 was also determined. In general, it was found that compounds 1-5 were less active than cisplatin and carboplatin against MCF-7 and HeLa cell lines (except for 1, which was found to be more active than carboplatin against the MCF-7 cell line). Compounds 1 and 3 were found to be significantly more active than cisplatin and carboplatin against the HEp-2 cell line.