In this paper results concerning emulsion copolymerization of vinyl acetate (VA) and butyl acrylate(BA) are presented. The mechanisms of particle nucleation and growth are studied by measuring perticle size and particle number in different monomer ratio copolymerization. The results show that increasing VA content in comonomer mixture causes a larger particle number and smaller particle size. The dependences of particle size and particle number as well as particle morphology upon monomer conversion are also discussed.