Spherical polystyrene powders coated uniformly byγ-Fe2O3 or RuO2 were obtained by means of a direct suspension polymerization. Starting reactant mixture was a complex disperse system comprising a fine powdered material, droplets of styrene monomer containing lauroyl peroxide as an initiator; and an aqueous medium. By varying the ratio between monomer and water, amount of powders as well as of the initiator, factors dominating particle size, volume fraction-of fine powders adhered and the degree of polymerization were elucidated