The development of polymer nanocomposites is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. The nanocomposites were prepared from unsaturated polyester (UPE) mixed with a different percentage (10, 20, and 30%) of silica nanoparticles. TGA and DSC curves were obtained from the thermal degradation computed by using Coast-Redfern technique. Kinetic and thermodynamic parameters were studied for all specimens were presented a good linear correlation coefficient close to unity using Minitab 16. Experimental work was showed that the degradation of composites that obtained from thermal gravimetric analysis was slower than the resin. Also, the decomposition under the oxidative environment was much faster than the inert environment. The enhancement of stability was attributed to silica content.