In this work hydrolitytic and photolytic degradation of three anthelmintics: albendazole, febantele and praziquantel were investigated. The hydrolytic degradation of the three antihelmintics was examined in buffer solutions with different pH-values and at different temperatures. Photolytic degradation of pharmaceuticals was investigated under simulated sunlight in MilliQ water, and also the influence of anorganic ions was examined (Cl-, NO3-, SO42- and PO43-) in concentrations common for environmental water. Results of hydrolytic degradation showed different behaviour of all three pharmaceuticals. Praziquantel was resistant to hydrolitic degradation at all three investigated pH-values while albendazole has shown to be stable at pH 4 and 7, and febantel was unstable at all three pH-values. The hydrolytic degradation of albendazole and febantel depends on temperature, and it is proportional to temperature. Hydrolytic degradation is faster at higher temperatures. In all cases hydrolytical degradation of albendazole and febantel followed first-order kinetics with the coefficient of determination > 0.96. Two degradation products were identified for hydroliticaly instabile pharmaceuticals; however, further investigation is needed to determine their exact structures. Also, direct and indirect photolytic degradation of febantel and praziquantel under simulated sunlight irradiation was investigated. It has been demonstrated that photolytic degradation is not an important degradation process since both investigated pharmaceuticals were stable.