A heterocoagulation strategy based on colloidal steric stabilization theory has been developed, through which polystyrene (PS) and silica (SiO2) particles without any surface modification or functionalization self-assembled rapidly via solution to afford nanocomposite particles with raspberry-like morphology. The formation mechanism is fully studied on the basis of a thermodynamic analysis. The soluble stabilizer and the solvent quality are the main determining factors, which have a significant influence on this self-assembly process and the silica coverage of resultant composites. The relative size of PS to SiO2 candidates also has the effect of control on the extent of self-assembly. Furthermore, this strategy can be applied to fabricate a broad range of composite materials, including PS/TiO2, PS/AgI, as well as PS/PS composites.