Abstract: Functional polymer microspheres with micron size, due to their excellent properties such as small size, narrow size distribution and kinds of functional groups, have gained broad applications in biomedicine, catalyst, bioengineering, separating engineering and information technology. In the present paper, uniform polystyrene (PS) microspheres with average size of 3.85 μm were prepared by dispersion polymerization. Through adding second monomer acrylonitrile (AN) to initiate dispersion copolymerization, uniform P(St-AN) copolymer microspheres with average size of 4.02 μm were prepared. These two kinds of polymer microspheres were characterized by morphology and size analysis, FT-IR and DSC. The results showed that acrylonitrile groups were uniformly grafted on the surfaces of polystyrene microspheres and enhanced the polarity of the surfaces. For the P(St-AN) copolymer micro-spheres, average diameter D=4.02 μm, standard deviation δ=0.30 μm, coefficient of variation ε=0.075 and glass transition temperature Tg=86.5 ℃.