Abstract: The pig liver sample (2.000 g) was added into 20 mL of 0.2 mol·L^-1 HCl solution for ultrasonic extraction at 25℃ for 40 min. Then 200 μL of 70%-72% (φ) HClO₄ solution was added and mixed well. The mixture was centrifuged at low temperature and high speed. 10 mL of n-hexane was added into the supernatant and the mixture was shaken evenly, and centrifuged. The organic phase was discarded, and 10.00 mL of the extract was taken on an activated MCX solid phase extraction column, rinsed with methanol (1+1) sloution and eluted with a mixture of ammonia-methanol (4+96). The eluate was concerntrated to near dryness by nitrogen blowing, and made up to 1 mL with methanol. After filteration with 0.22 μm filter membrane, the filtrate was separated on a Waters ATLANTICS C₁₈ chromatographic column (2.2 mm×150 mm, 5 μm), with a mixture of 0.1% (φ) formic acid solution and acetonitrile as mobile phase for gradient elution. Electrospray ion source and multiple reaction monitoring mode were selected for mass spectrometry analysis. Linear relationships were found between the peak areas of 12 β₂-agonists with the corresponding mass concentration within definite ranges, and the detection limits (3S/N) were in the range of 0.01-0.1 μg·kg^-1. Values of recovery obtained by standard addition method were in the range of 70.0%-120%, and RSDs (n=6) of intra-day and inter-day were less than 12%.