The aim of the master thesis focuses on the flexographic printing field with the purpose to investigate the efficiency of Fenton process for the treatment of yellow flexographic dye, as well as to investigate the impact of various process conditions. Fenton process is one of the most efficient oxidation processes used for treatment of wastewater with high content of heavy degradable compounds. It is based on the generation of hydroxyl radicals from hydrogen peroxide with iron ion as catalyst in an acidic medium and environmental conditions. During the experiment, pronounced influence of pH in the heterogeneous Fenton process was established, while the influence of other factors is negligible. It has been found that a pH decreasing results within increase of decolorization efficiency of the synthetic dye solution.