Silver - polystyrene polyvinylpyrrolidone nanocomposites were synthesized by polymerization which was induced by gamma-ray irradiation. Silver (Ag) nanoparticles were embedded in the polystyrene via subsequent reduction of Ag+ by gamma-ray irradiation. Dispersion of Ag nanoparticles was achieved using polyvinylpyrrolidone as a dispersing agent. The morphology and particle size of the new silver/polystyrene/polyvinylpyrrolidone nano composite was studied by ultraviolet-visible spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction analysis and thermal gravirnetric analysis. The prepared nanocomposites showed improved thermal stability. The TEM images demonstrate that well-dispersed Ag nanoparticles were embedded in polystyrene polyvinylpyrrolidone. According to TEM analysis, the size of the nanoparticles was found to be in the range of 15-45 nm. TEM images showed the favored shape of the nanoparticles as spherical. TGA indicated that the thermal stability of polystyrene is enhanced when loaded with Ag nanoparticles and this is clear from the data obtained and the values of the activation energy. This method constitutes a promising way to prepare versatile inorganic-organic polymer nanocomposites. The applied method is both simple and inexpensive and does not use toxic chemicals, unlike other chemical methods.