An attempt was made to develop new water-soluble antitumor Pt(ll) complexes containing ethylenediamine, and their structures were determined by infrared spectroscopy, $^{13}C$ nuclear magnetic resonance and elemental analysis. Their antitumor activities in vitro against L-1210, p-388 leukemia cells and M-14 melanoma cells were investigated and acceptable antitumor activity was found as compared with cisplatin.