One of the most significant environmental challenges nowadays is the rising manufacturing of non-biodegradable polymer wastes like polystyrene. In order purpose of manufacture environmentally friendly polystyrene that easily decomposes, a solvent approach was used to create polystyrene based zinc oxide- graphite composites. The surface morphology and materials contained in the modified polystyrene were evaluated by scanning electron microscopy-energy dispersive X-ray analysis to verify the dispersion and distribution of the nanoparticles by scanning electron microscopy and the material contents by energy dispersive X-ray analysis. While the crystal structure, chemical bonds, and functions were determined by X-ray Diffraction and Fourier transform infrared, no change in the chemical structure occurred in polystyrene. Thermogravimetric analysis was used to assess the thermal decomposition. And its results found that the temperature of the decomposition was 46.78° lower in zinc oxide and graphite-based polystyrene composites than in pure polystyrene. It came to light that the presence of zinc oxide nanoparticles causes phase separation and consequently impacts the thermal behaviour of graphite-based polystyrene composites. The phase separation was demonstrated by the Thermogravimetric curves showing two degrading steps. This satisfies the urgent demand to synthesize polystyrene that is eco-friendly and easy to thermally decomposition, as well as easy to recycle, which benefits both the environment and the commercial side.