Abstarct: In this research Polymethyl methacrylate/Ag-CeO2 Nanocomposite was prepared in three stages. First,nano cerium oxide was obtained from reaction of Ce(OAC)3. XH2O in the presence of surfactant Cetyl trimethyl ammonium bromide (CTAB), in the alkaline environment. Then Ag-CeO2 nano-composite was obtained by reduction of AgNO3 by glucose in the presence of cerium oxide. In the third phase of spread Ag-CeO2 in mtylmtakrylat and to assist the initiator benzoyl peroxide, polymer nanocomposite Ag-CeO2 / poly (mtylmtakrylat) was prepared. Cerium oxide nanoparticles , nano composites Ag-CeO2 and polymer nanocomposite Ag-CeO2 / poly (mtylmtakrylat were identified and 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). Thermal stability of the nanocomposite was assessed by the techniques of simultaneous thermal analysis (TG/DTA) and Differential Scanning Calorimetry (DSC). Photocatalytic activity was investigated of nanoparticles and polymer nanocomposite organic dye Methyl Orange degradation.The results of thermal analysis showed an improvement in nanocomposite thermal property and glass transmission temperature, compared with Polymethyl methacrylate . Cerium oxide nanoparticles and nanocomposite Ag-CeO2 were showed good photocatalytic activity in the degradation of methyl orange.