Abstract: Sample of the medicine was extracted with acetone ultrasonically,and the extract was evaporated to dryness heated at below 50 ℃ in a water bath under reduced pressure.The residue was dissolved in 2.0 mL of the mixture of H2O+acetic acid+acetonitrile (mixed in the ratio of 49+1+50),which was used as mobile phase later,and used for LC-MS/MS determination.The Kromasil C18 was used as stationary phase in liquid chromatography.In the MS/MS analysis,APCI was used as ion source,and modes of SIM and SRM with positive ion scanning were taken for the quantitative and qualitative testing of aristolochic acid A.The M+NH4+ (m/z 359) was taken as the mother ion,and the fragment ion M-NO2+H+ (m/z 298) was taken as quantitative and qualitative ion.The fragment ion M-CO2+H+ (m/z 296) was taken as auxiliary qualitative ion.Linearity range for determination of aristolochic acid A was found between 0.2 and 10.5 mg·L-1.The lower limit of determination (10S/N) found for the method was 0.07 mg·L-1.Test for recovery was made at 3 different concentration levels,values of recovery were found in the range of 89%-95%,with RSD′s (n=6) less than 5.5%.