We report a flexible method to functionalize highly transparent graphene oxide (GO) film with gold nanoparticles (AuNPs). Nonlinear absorption and refraction of the hybrid films are measured, which are strongly enhanced and tunable by different AuNP concentrations compared to both GO and AuNP-only samples. The enhanced nonlinearity is due to the effective functionalization of the hybrid films, which is verified by the ultraviolet-visible and Fourier-transform infrared spectra. Our low-loss hybrid GO-AuNP films provide a solid-state material platform for diverse nonlinear applications. The functionalizing method can serve as a universal strategy to manipulate the physical properties of hybrid GO.