The size effects of SrTiO3 nanoparticles are investigated by Raman spectroscopy and UV-Visible absorption spectra with changing grain size in the range of 10—80 nm. It is found that the intensity for the first-order TO2 mode increases significantly as the grain size decreases from 80 to 10 nm. Such behavior suggests the presence of the micropolar regions on the grain boundary induced by the enhanced surface-defect dipoles. Moreover, the first-order TO2 and TO3 modes show red-shifts, indicating the increase of the Ti—O bond-length with decreasing grain size of SrTiO3 nanoparticles. The softening of the Raman mode is consistent with the lattice expansion investigated by XRD. In addition, the UV-Visible absorption spectra indicates the enhancement of absorption due to surface distortion states and hence the lattice expansion, which results in the increase of Eg-value.