A rapid, sensitive and reliable ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed and validated for the simultaneous quantitation of pyrantel (PYR), praziquantel (PRA), febantel (FBT) and its active metabolites, fenbendazole (FEN) and oxfendazole (OXF) in dog plasma. Fenbendazole-D3 (FEN-D3) was used as an internal standard (IS). The analytes and IS were prepared using simple protein precipitation (PP) combined with liquid-liquid extraction (LLE). Chromatographic analysis was performed on UPLC BEH C