Abstract: A series of P(MMA-St)/P(BA-EA) acrylic latex interpenetrating polymer networks (IPNs) were prepared by employing emulsion polymerization method. Stained by a PTA (phosphotungstic acid) negative staining technique, latex particles were observed by using transmission electron microscope (TEM) to study their micro-structures and reaction processes. The results show that mass ratio of networks, swelling time and swelling style are all critical factors which influence the microstructures of latex particles greatly. The mass ratio of two networks determines the size of latex particles. Meanwhile, swelling time had dramatic effects on the thickness of the shell structure of IPNs, and swelling style affected the properties of latex films.