Conventional wastewater treatment plants (WWTPs) partially eliminate micropollutants present in domestic and industrial discharges (Martin-Ruel et al., 2010; Choubert et al., 2011). However, some molecules still occur in effluents of WWTPs at concentrations close to 0.1 μg/L for some pesticides (e.g. diuron) and pharmaceuticals (e.g., carbamazepine, sotalol, diclofenac). The potential hazard of these compounds requires the development of new processes (tertiary) to anticipate possible regulation changes. This poster focuses on study of 11 compounds (pesticides and pharmaceuticals) during degradation process in tertiary treatments such as ozonation or photodegradation. The aim of this communication is to present our analytical methodology to identify degradation products (DP) created under controlled conditions during lab-scale experiments. Both direct and indirect ozonation of spiked WWTP effluent at about 1 µg/L was driven on a lab-scale apparatus at two different O3 concentrations (4.3 and 9.5 gram per gram of dissolved organic carbon). Photodegradation was studied in laboratory with ultrapure water spiked at 10 µg/L using a light box equipped with a xenon lamp. Analysis of parent and degradation products were performed on a Waters ACQUITY H-Class UPLC system coupled to Xevo G2-S high resolution mass spectrometer using a quadrupole-time of flight technology. The separation was performed on a C18 HSS-T3 column (100mm x 2.1mm, 1.7µm) after direct injection. Acquired centroid raw data were processed quantitatively for parent compounds using TargetLynx and qualitatively for degradation products identification using ChromaLynx applications manager for MassLynx 4.1 software. Such strategy combined a classical targeted analysis with quantitative approach and a retrospective database comparison for suspected-target screening of more than 150 potentially DPs. Results and discussion are focused on criteria and clues to identify DP. Scoring of evidences is based on proposed identification confidence levels described by Schymanski et al. (2014).