Four platinum(II) and 4 platinum(IV) complexes with the structures [PtL2Cl2], [PtL2I2], [PtL2Cl4], and [ PtL2Cl2( OH)(2)] ( L = 5(6)-non/orchloro-substituted-2-hydroxymethylbenzimidazole ligands as "non-leaving groups"), respectively, were synthesized and characterized by their elemental analyses, and IR and H-1-NMR spectra. In vitro cytotoxic activities of the platinum( II) and platinum( IV) complexes were tested against the human MCF-7 ( breast cancer) and HeLa ( cervix cancer) cell lines using the cell culture method. In general, the platinum( II) complexes were more active than the corresponding platinum( IV) complexes. The complexes, which were found to be less active than cisplatin, exhibited cyctotoxicity comparable to carboplatin on the human MCF-7 and HeLa cell lines.