Photolytic reactions are often complex, involving various competing or parallel pathways and leading to multiple reaction products. Removal of anthelmintic drugs (AD) - levamisole (LEV), albendazole (ABZ), praziquantel (PZQ), febantel (FEBA) from water and their photodegradation products with reverse osmosis (RO) and nanofiltration (NF) membranes were investigated in this work. Simulation of photodegradation of ADs was carried out under laboratory conditions with UV lamp at a wavelength of 254 nm for 4 h. Reverse osmosis (LFC-1 and XLE) and tight nanofiltration (NF90) membranes showed good removal (> 83%) of anthelmintic drugs in binary solutions and in mixture. Other nanofiltration (NF270, NF and DK) membranes had rejection between 22 and 45% for smaller drugs (LEV and ALB) and > 90% for PZQ and FEBA. These results show that main rejection mechanism in binary solutions was size exclusion and in mixture additional physico-chemical interactions had influence. After the UV treatment anthelmintic drugs were degraded into several photodegradation products (5 for LEV, 2 for ABZ, 1 for PZQ and 8 for FEBA). Reverse osmosis and NF90 membranes removed > 95% of all photodegradation products (except FEBA, around 70%) and other nanofiltration membranes between 33 and 99.99%. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.