The effects of solar radiations on physical properties and molecular structures of 200 nm polystyrene nanospheres (PSN) coated on silicon wafer were explored by field emission scanning electron microscope (FESEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. It is revealed the particles shape of PSN changed from spherical to dumbbell-like shape after solar irradiation. Reduction of the PSN size as much as 23.79% after 5 minutes exposure was also observed in PSN particles. We believed that some of the phenyl moieties of polystyrene broke down to facilitate carbon-carbon cross linkage bonds intra- as well as inter-PSN particles and were shown by ATR-FTIR spectrums. These results proven the shrinkage of PSN particles were caused by the change of the molecular structure of the irradiated PSN to be much more dense material.