FIELD: medicine, oncology, pharmacy. SUBSTANCE: invention claims a pharmaceutical composition as an aqueous solution containing 1-20 mg of carboplatin/ml, 1,1-cyclobutanedicarboxylic acid and/or its salt taken in the amount 0.1% of carboplatin weight, not less, being immediately before the composition preparing. The decrease of content of an active substance in 2.5 year is 1.8-1.9%. Invention can be used for preparing antitumor preparations. EFFECT: increased stability of carboplatin solution in storage. 1 tbl
