Colloidal gold nanoparticles were immobilized on to a solid surface through a bifunctional,elf-assembled monolayer, forming a sandwiched structure in the form of [gold nanoparticulate film]/[self-assembled monolayer]/[solid surface]. Thus prepared model system was used to study the mechanisms of surface enhanced Raman scattering(SERS). A preliminary result is given in this paper on particle size and potential dependencies of surface enhancement of Raman scattering.