The presence of drugs in the environment is increasing daily due to the increasing applications in medicine and veterinary medicine, and because of their negative impact on the environment it is necessary to remove them effectively. For the purpose of removing anthelmintics from water, reverse osmosis (RO) membrane process was used in this study. The analysis showed that removal efficiency is more than 99% for listed anthelmintics. Results of the FTIR analysis indicated that there was no significant interaction between the membrane and anthelmintics. However, one of the major disadvantages of membrane processes is the need to treat the retentate. The aim of this study was to investigate the effectiveness of adsorption as anthelmintics (praziquantel, febantel, and their mixture) removal method from the RO retentate. The adsorption was carried out in a column with a fixed bed of granular activated carbon (GAC). Analysis of the GAC sample showed a large active surface area (809 m^2/g) as a result of mainly microporous sample structure. In this study it was explained the effect of flow rate (17.1–125.1 mL/min), bed height (10 and 20 cm), mixture and initial solution concentration (5.72–10.2 mg/L) on the behavior of breakthrough curves. For the description of the adsorption equilibrium there were tested two models of adsorption isotherms. Better fitting of experimental data and models was perceived by using Freundlich's isothermal equations. The monolayer adsorption capacity was determined from the Langmuir model and it was 0.81 mg/g.