Abstarct: In this research Poly(methylmethacrylate) / SnO2 Polymer Nanocomposite was prepared in three stages. First, SnO2 was prepared from reaction of SnCl2.2H2O with NH4(OH) in the presence cetyl¬trimethyl¬Ammonium¬Bromide (CTAB) as surfactant.Then, the surface of nanoparticles was modified in order to obtain better dispersing and proper compatibility in organic media by 3-(Trimethoxysilyl)propyl methacrilate. These Modified Nanoparticles, were dispersed in methylmethacrylate monomer and through bulk polymerization, nanocomposite Polymethylmethacrylate/SnO2 nanocomposite was prepared. SnO2 nanoparticles and polymer nanocomposites were identified and their structurs were confirmed by the techniques of Fourier Transform Infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and Energy-dispersive X-ray (EDA) techniques. Thermal stability of the nanocomposite was assessed by the simultaneous thermal analysis (TG/DTA) and Differential Scanning Calorimetry (DSC) techniques. studying of nanocomposite compared with Poly(methylmethacrylate).