Abstract: [Objective] To establish a HPLC method for determination of oxymatrine content in a botanical acaricidal bath agent for external use.[Method] The separation was performed with the commercially available chromatographic column of Waters XBridge C18 (4.6 mm×150 mm,5 μm).Methanol-0.05 mol/L sodium dihydrogen phosphate (containing 0.5% sodium perchlorate)(15:85) was used as mobile phase,the flow rate was 1.0 mL/min,the detection wavelength was 220 nm,the sample volume was 10 μL,and the column temperature was 30 ℃.[Result]There was a good linearity between the peak areas and the mass concentrations of oxymatrine in the range of 0.020 592 - 0.457 47 mg/mL (Y=5.72e+006X+1.13e+004,R^2=0.9998).The RSD of the precision test (n=6),repeatability test (n=6) and recovery test was 0.3%,1.0% and 1.6%,respectively.[Conclusion] The established HPLC method has the advantages of simplicity,speed,good stability and high repeatability,and can be used in quality control of the botanical acaricidal bath agent for external use.