A method for the production of a reaction coordination compound of a platinum complex and a polymer having carboxyl groups in its side chains, where it is used as a starting material for the platinum complex bis (nitrate) 1,2- cyclohexanediamine) platinum (II) or diacuo (1,2-cyclohexanediamine) platinum (II), all of which are substantially free of silver ion, and a block copolymer represented by the following general formula (1) or is used as the polymer (2): ** Formula ** wherein R1 represents a hydrogen atom or a linear or branched, substituted or unsubstituted C1-C12 alkyl group； L1 and L2 each independently represent linker groups, R2 represents a methylene group or an ethylene group, R3 represents a hydrogen atom, an amino group protecting group, a hydrophobic group or a polymerizable group, R4 represents a hydroxyl group, a protected carboxyl group as formed together with the -CO terminal group, or a hydrophobic group； R5 independently represents a hydrogen atom, an alkali metal ion or a carboxyl group protection group； m represents an integer from 5 to 20,000, n represents an integer from 2 to 5,000, and x represents an integer from 0 to 5,000, with the proviso that x is not greater than n, and a hydrogen atom or an ion of alkali metal supposes 50% or more of nx and x R5, the method comprising a step of carrying out the reaction in an aqueous medium under the conditions in which the platinum complex and the block copolymer mutually form a coordination compound , and a recovery step of such coordination compound thus formed from the reaction mixture, wherein the ratio of platinum atoms in the platinum complex to the carboxyl groups in the block copolymer in the reaction is set from 0.475 or more. to 0.6 or less, and the concentration of the platinum complex in the aqueous medium in the reaction is set at 4.62 mM or less.Un método para la producción de un compuesto de coordinación por reacción de un complejo de platino y un polímero que tiene grupos carboxilo e
