In this paper, the preparation and characterization of ZnO nanofillers from polystyrene (PS) polymer waste for use as reinforcement was presented. This was done to achieve a better means of upcycling polymer wastes that have become social menace in recent times. The PS/ZnO nanofillers was synthesized through the hydrothermal synthesis of nanocomposites in an enclosed reactor. The reactor was kept in an oven at a specified temperature for a period. A product obtained was characterized using Fourier transform infrared (FTIR) analysis and Particle size analyser (PSA). The FTIR was utilized to determine the functional groups present in the synthesized nanofillers. The Particle size analyser was used to determine the distribution of particle size within the polymer matrix. The absorption peak obtained in the FTIR analysis confirmed the presence of ZnO in the synthesized material and the results from particle size analysis showed that about 80% of the particle was accommodated within the whole sample.