cis-Malonato[(4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1,3-dioxolane]platinum(II)(SKI 2053R), an antitumor platinum complex, was selected for clinical evaluation on the basis of its experimental antitumor and toxicologic profiles in preclinical studies. These studies were performed to obtain information on its toxic signs, orgnas which are mainly affected, and to estimate its lethality in mice and rats given SKI 2053R through two routes of administration. In male and female rats given a single intragastrical dose of SKI 2053R, we estimated that $LD_{50}$ values were over 3.00g/kg, respectively. In male and female mice given a signle intragastrical dose of SKI 2053R, we estimated that $LD_{50}$ values were 2.44g/kg and 1.59g/kg, respectively, In a single intraperitoneal dose of SKI 2053R, we determined that $LD_{50}$ values of male and female rats were 227mg/kg and 182mg/kg, and those of male and female mice were 198mg/kg and 207mg/kg, respectively. In gross and histopathological examinations on dead animals, we found that kidney and liver were mainly affected.