Nanoparticles with projection coronas were prepared by the one-step dispersion terpolymerization of styrene, acrylonitrile, and poly(ethylene glycol) monomethacrylate in ethanol-water solution, and their morphologies were controlled. When the mole composition of acrylonitrile to the total monomers C-AN was 0.49-0.66, electron microscopy showed that the nanoparticles were spherical and had a number of projections on the surface. A C-AN of more than 0.66 yielded no nanospheres, and a C-AN smaller than 0.49 yielded projection-free nanospheres. The morphology of the nanospheres could be controlled by changing the reaction conditions, and some conditions yielded a regular arrangement of uniform projections on the surface similar to that seen in some coronaviruses. X-ray and spectroscopic studies suggested that the projections might be formed as a result of the nonequilibrated swelling of acrylonitrile and poly(ethylene glycol) domains on the surface.