PURPOSE:To facilitate the formation of polymer particles of a large diameter, by finely dispersing a polymerizable monomer in an aqueous medium to prepare a dispersion containing dispersed monomer drops having a specified number- average particle diameter, mixing this dispersion with a dispersion of seed particles and polymerizing the monomer. CONSTITUTION:A polymerizable monomer (e.g., styrene) is finely dispersed in an aqueous dispersion to prepare an aqueous polymerizable monomer dispersion which has a number-average particle diameter of dispersed liquid monomer drops not more than the number-average particle diameter of seed particles and satisfies the relationship of the formula, wherein Dm is the number-average diameter of the dispersed liquid monomer drops in a metastable state and D is the desired number-average particle diameter of the final polymer particles. This monomer dispersion is mixed with a dispersion of seed particles (e.g., polystyrene particles) to effect absorption or adsorption of the polymerizable monomer by the seed particles. The polymeizable monomer is polymerized in the presence of a polymerization initiator to obtain large polymer particles having a particle diameter of 0.1-500mum.