The nonlinear optical properties of gold nanoparticles with different densities of particles on indium-tin oxide (ITO) substrates of different origins are investigated. The coherent photoinduced nonlinear optical effect at 1.32 mu m reveals a marked dependence on the interparticle distance and density. The decrease of the interparticle distance with the increase of Au nanoparticle density favours the photoinduced optical second harmonic generation. The maximal second-order optical susceptibility attained at a wavelength of 1.32 mu m corresponds to the value of about 4.56 mu m V-1. The predominant role of the interface between the Au nanoparticles and the ITO substrate is shown.