In this paper theeffect of ZnO dopant on the nonlinearoptical behavior of TiO2-PMMA Nano composites films was studied. TiO2-PMMA Nano composites films were prepared using solution casting method then doped with different amounts of ZnO nanoparticles. Z-Scan measurements were performed to obtain the nonlinear optical response of these samples at 1064nm using CW Nd-YAG laser. The addition of ZnO nanoparticle into the Nano composites showed a great enhancement in the nonlinear optical response and decreasing in limiting threshold (10 mW)as the dopants concentration increased.