Abstract A novel series of platinum (II) complexes was synthesized and the complexes were evaluated for their in vitro cytotoxicity against four human cancer cells lines. Five platinum complexes showed activity against at least one tumor cell line. Complexes 3 and 6 were promising, being active, at micromolar concentrations, against all the assayed tumor cell lines. Compound 3 was selected for further studies in mice with Ehrlich solid tumors and it was able to reduce the rate of tumor growth significantly during the first seven days. However, at the end of the experiments, there was no significant difference between the group of animals treated with 3 and the control group. The low solubility of the compound in the assay conditions can explain, at least in part, these results.