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A rapid simultaneous assay was developed for determining 63 veterinary drugs in bovine, porcine, and poultry muscles by on-line solid phase extraction (on-line SPE)/high-performance liquid chromatography/tandem mass spectrometry (MS/MS). The drugs were extracted from muscle samples with acetonitrile-methanol (4: 1, v/v). The extracts were evaporated, and the residues were dissolved with acetonitrile-water (I : 1, v/v). The samples were injected into an on-line SPE column packed with Oasis HLB using 0.1% formic acid as a mobile phase, to separate drugs from interfering substances and retain them on it. The drugs were introduced onto an analytical column using 0.1% formic acid-acetonitrile in a gradient mode by column switching and directed into MS/MS. Under the optimal analytical conditions, the repeatability of the retention time and the peak area of standard compounds were less than 1% and 12%, respectively. The recoveries of 63 drugs from muscle spiked at 20 ng/g were 45.8 similar to 153%. The detection limits were less than or equal to 10 ng/g.