Abstract: The invention relates to platinum complexes of the following general formula: ##STR1## wherein R.sub.1 and R.sub.2 represent alkyl radicals with 1 to 18 carbon atoms, or R.sub.1 or R.sub.2 represent a hydrogen atom and R.sub.2 or R.sub.1 can represent an alkyl radical or a ##STR2## in which R.sub.3 is a hydrogen atom or the ##STR3## radical or an acyl radical, and x=1 or 2. These compounds can be produced by reaction of an alcohol solution of a 5,8-dihydroxyl-1,4-naphthoquinone of the following formula: ##STR4## in which the substituents R.sub.1 and R.sub.2 have the aforementioned meanings, in the presence of a concentrated aqueous ammonia solution, which adjusts the pH over 7, with K.sub.2 PtCl.sub.4 at room temperature. These platinum complex compounds are characterized by a good antitumor effect with low toxicity.