Au-TiO2 composite films with Au atom content varying from about 15% to 82% are prepared by co-sputtering technique. Both open- and closed-aperture Z-scan of the samples are performed in the femtosecond time region.A conversion of the nonlinear absorption from negative to positive is observed as the Au atom content increases due to the saturation of reverse saturable absorption. The nonlinear refractive index γ and effective nonlinear absorption coefficient βeff at the Au atom content of 54% are measured to be 1.6 × 10-2 cm2/GW and -2.6 ×103 cm/GW, respectively. The corresponding third-order optical nonlinearity χ(3) is about 6.3 × 10-8 esu.