Objective: This study aimed to synthesize and evaluate the cytotoxic activities of four platinum(II) complexes with 2-substituted or nonsubstituted 1H-benzo[d]imidazole and 1H-1,3-diazole derivatives as carrier ligands (L1-L4), which may have potent cytotoxic activity and low side effects. Material and Method: K1-K4 complexes were synthesized by heating and mixing K2PtCl4 and the appropriate L1-L4. The chemical structures of K1-K4 were elucidated by Infrared and 1H Nuclear Magnetic Resonance spectroscopic methods. In vitro, cytotoxic effects of K1-K4 complexes against prostate (DU-145), endometrial adenocarcinoma (Ishikawa), and breast cancer (MCF-7) cell lines were tested by the MTT method. Result and Discussion: According to the IC50 values of the tested cell lines, K1 and K2 derivatives bearing unsubstituted 1H-benzo[d]imidazole (L1) and 1H-1,3-diazole (L2) were found to be the most effective compounds among these synthesized complexes.