In this research studies, a surfactant-free emulsion polymerization method was employed to synthesize nano-ZnS/polystyrene composite particles. In this approach, 2-(dimethylamino)ethyl methacrylate (DMEMA) was used as the auxiliary monomer to co-polymerize with styrene, which provides the locations for coordinating with Zn2+ ions, and finally leads to the formations of ZnS/PS composite particles. It was observed that the resulting nano-ZnS/PS composite particles had the raspberry-like morphology when the process was conducted under low DMEMA content. Upon increasing the DMEMA content, the morphology for ZnS changed to become hollow ZnS micro-spheres. In the method proposed in this study, stable emulsion was successfully obtained under a surfactant-free environment. The possible mechanisms for the formation of the different mechanisms are presented.