Using 1.064 μm wavelength laser pulses, the photopolymerization of C 60 films on a polycrystalline Ag surface under ultrahigh vacuum (UHV) environment is investigated by optical second harmonic generation (SHG) method. It is found that the intensity of the SHG signals from C 60 films increases with the extension of exposure time under ultraviolet light, and finally reaches to a saturation value. We suggested that the enhanced second harmonic generation from photochemically modified C 60 films is induced by the reinforce of bulk electric quadrupole polarization and magnetic dipole.