Pharmaceuticals are used for the purpose of preventing or treating diseases in humans and animals, as well as growth promoters in veterinary medicine. Due to the widespread use, they are found in discharges after wastewater treatment, in surface waters, soil and tap water. One of the most frequently detected pharmaceutical compounds in the environment is diclofenac, a non-steroidal anti-inflammatory drug, which is easy bioaccumulated in the tissues of aquatic organisms. In order to prevent further adverse effects of pharmaceuticals, including diclofenac, it is necessary to develop new treatment systems, which are sometimes a combination of the existing system. As an effective and relatively simple solution are Advanced Oxidation Processes (AOPs) which, often in combination with biological treatment, can completely degrade pharmaceuticals in water. Among them, heterogeneous photocatalysis is a very promising method, which can be used for degradation of various organic pollutants in water and air. The aim of this paper was to investigate the change of water quality indicator during photocatalytic degradation of DCF with a TiO2-SnS2 photocatalyst under simulated solar irradiation. The heterogeneous photocatalyst was prepared by a hydrothermal method, with a 27.6% weight fraction of SnS2 within the photocatalyst, added with the aim of increasing photocatalytic activity and stability under solar irradiation. Degradation of diclofenac in model wastewater was carried out at various times to establish the optimum time of reaction and the percentage of removal and conversion of diclofenac and adsorbed by-products in solution. After the analysis, the results showed a great contribution of the adsorption mechanism as well as the oxidative degradation in the total efficiency of the applied solar/TiO2-SnS2/H2O2 process with 89.98% of removed diclofenac and 64.07% of removed total organic carbon, respectively. The achieved conversion of DCF was 88.55% while the mineralization amounted to 34.86%. The Solar/TiO2-SnS2/H2O2 process performed under optimal conditions shows increased biodegradability, but also the reduction of toxicity after a 3,5 hour process.