In this paper we report the results of polarization resolved hyper-Rayleigh scattering measurements of coppernanoparticles of 5−55 nm size. The polar plot of polarization-resolved second harmonic intensity againstpolarization angle from the copper nanoparticles resembles the pattern seen from a dipolar source. The measuredfirst hyperpolarizability values scale quadratically with the particle size, which implies that the second harmonicresponse from the copper nanoparticles results from symmetry breaking at the surface of the particle ratherthan in the bulk.