Polymethyl methacrylate-zinc oxide (PMMA/ZnO) nanocomposites with different ZnO morphology and quantities were prepared by insitu curing of MMA/PMMA used in denture base material in the presence of ZnO nanostructured materials. The composition, structure, and morphology of the nanocomposites were characterized by Fourier-Transform infrared spectra (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The effect of ZnO morphology and contents on the mechanical properties including impact, flexural, and hardness was studied. The results demonstrated that the mechanical and thermal properties of denture base materials were improved by incorporation of nano-sized ZnO into the polymethyl methacrylate matrix. The impact strength was highly improved upon using ZnO nanotubes. However, the flexural strength was improved using ZnO nanospheres.