Abstract Several dipeptide complexes of the form K[Pt(x-gly or gly-x)Cl], where x-gly or gly-x stands for a dipeptide anion (where x is glycine, alanine, valine, or leucine) moieties, were synthesized, purified, and characterized by various analytical and spectroscopic techniques (13C, 195Pt NMR and MS(FAB)). The complexes of the form K[Pt(x-gly)Cl] were pale brown and those of K[Pt(gly-x)Cl] were light yellow in solid form or in solution. The former was more labile than the latter in H2O solution. Growth inhibition assays of K[Pt(alagly)Cl], K[Pt(glyala)Cl], and cis-diamminedichloro platinum(II) (Cisplatin) against methylcholanthrene induced Meth A fibrosarcoma (Meth A) solid tumors transplanted in BALB/c mice were measured. In mice in the group administered K[Pt(glyala)Cl] doses of 26 mg kg−1 d−1, 28.9% of slight growth inhibition was observed. The side effects related to the decrease of body weight were mild. Cisplatin did not show any antitumor activity under the present administration conditions. The toxicities of the dipeptide complexes against normal mouse bone marrow cells were measured. All of them exhibited toxicity against bone marrow cells, but K[Pt(alagly)Cl] and K[Pt(glyala)Cl] were 1000 times less toxic than Cisplatin.