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A reliable method for the simultaneous determination of toltrazuril and its main metabolites (toltrazuril sulphone and toltrazuril sulphoxide) in chicken and pig skin + fat was developed and validated. Analytes were extracted from skin + fat with acetonitrile. The crude extracts were subjected to liquid-liquid extraction with n-hexane, and then further cleaned using primary secondary amine and Oasis (TM) MAX solid phase extraction cartridges. Chromatographic separation by UPLC-UV was performed on a C18+ reversed-phase column with gradient elution. Relative recovery from the spiked samples ranged from 84.8% to 109.1%. Limits of detection and quantification for the analytes were within 25-37.5 mu g kg(-1) and 50-75 mu g kg(-1), respectively. The developed method has been successfully applied to the depletion study of toltrazuril drug residues in chicken skin + fat. The recommended withdrawal period with oral administration based on our research is 24.18 days. (C) 2014 Elsevier B.V. All rights reserved.