A platinum complex having a superior antitumor activity is disclosed. The platinum complex has a structure represented by the formula: ##STR1## wherein A and B independently represent a lower alkanoyloxy group which may have a halogen atom substituent, or in combination represent a group: ##STR2## wherein R.sub.1 and R.sub.2 independently represent a hydrogen atom, a hydroxyl group, or a lower alkyl group, or in combination with each other and with the adjacent carbon atom a cyclobutane ring, an...