A new preparation method for monodisperse polymer microspheres with a hydrophilic property has been investigated by utilizing an irradiation method. Hydrophilic microspheres were synthesized by radiation precipitation copolymerization using polyethylenglycol dimethacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and methacrylic acid monomer. The diameter of the microspheres prepared was 0.3-1 μm, in which the irradiation was carried out without catalyzer at room temperature for 1 hr at a dose rate of 10 kGy/hr with γ-rays from a Co-60 source. The diameter of the microspheres increased with increasing hydrophilicity of monomer.