The synthesis and biological activities of the platinum complexes of 2-aminomethylaziridine, 2-aminomethylazetidine, 2-aminomethylpyrrolidine, 2-aminomethylpiperidine as carrier ligands are described. The platinum complexes of 2-aminomethylazetidine and 2-aminomethylpyrrolidine are significantly effective against murine tumors. In particular, 2-aminomethylazetidine (1,1-cyclobutanedicarboxylato)platinum II (13) and 2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platin um II (16) exhibited potent antitumor activity and were soluble in water, and their antitumor activities against Colon 26 carcinoma (sc-ip system) were superior to CBDCA and comparable to CDDP.