The global need for plastics is continuously growing. The intensive use of plastics followed by later inadequate disposal is resulting in increasing amount of plastics in the environment. One of the biggest threats to the environment, especially to the aquatic one, are plastic particles smaller than 5 mm called microplastics (MP). Since applied methods for removing MP from water have not proven to be sufficiently effective, the application of advanced oxidation processes (AOP) has been considered. AOPs are processes in which highly reactive radicals are created. These radicals are able to decompose, organic pollutants from water, either partially or completely. AOP degradation of polystyrene (PS) microparticles in size 25 - 100 μm by UV-C/H2O2 and UV-C/S2O82- processes was studied. The experiments were conducted according to a full factorial design. FTIR spectroscopy was used for characterization of PS particles, while TOC and MS analysis were performed for analysis of the water solution. Based on the obtained results, a more efficient process for PS degradation and its optimal conditions were determined. According to the results, the more effective oxidizing agent for PS degradation is S2O82-. This study determined that only minimal decomposition of PS microparticles can be achieved by applying UV-C/S2O82- treatment and the effectiveness of the process depends on pH value of the medium, concentration of S2O82- and treatment duration.