Hyper-Rayleigh scattering (HRS) technique has been used to study second-order nonlinear optical (NLO) properties of some centrosymmetric metal and semiconductor nanoparticles. All the samples display big "per particle" first hyperpolarizabilities 'beta'_(par). For centrosymmetric particles the contributions of multipolar radiations are very important to their second-order NLO responses. The metal nanoparticles show 'beta'_(par) two orders greater than that of the semiconductor ones, which can be explained by the enhancement of surface plasma resonance (SPR). It also reveals that the HRS signals are very sensitive to metal nanoparticles' aggregation.