A method for the preparation of a dispersion of fine particles characterized in that the micelles are ones which have been formed in a aqueous medium with an amphiphilic block copolymer represented by the general formula PB and in which the shell of each micelle has been cross-linked with hydrophilic groups of the hydrophilic side chains wherein the particles formed are metallic particles having a reducing characteristic of metal ions. The general formula PB is: ##STR00001##