Aristolochic acids (I and II) are commonly found in medicinal plants such as Radix aristolochiae and have been reported to cause acute hepatitis and end-stage renal failure. The aim of this work was to develop a method for the analysis of aristolochic acids in medicinal plant/Chinese prepared medicine (CPM) using (CZE). The buffer used was 30 mM sodium tetraborate at pH 9.5, detection was at 254 nm, applied voltage at 18 kV and the temperature was set at 25 degrees C. The effect of ionic strength, pH, and applied voltage on the separation was investigated. The precision values (relative standard deviation, RSD, %) for the relative migration time and peak area or peak height for aristolochic acids I and II were found to be less than 0.3% and between 2.6 to 4.0%, respectively. The limit of detection for aristolochic acids I and II was found to be 1.2 and 0.9 mg/L, respectively. The proposed method using pressurized liquid extraction (PLE) with CZE was used to determine the amount of aristolochic acids in medicinal plants or CPM samples with complex matrix and the results were compared with high-performance liquid chromatography (HPLC). Method precision (RSD, n = 6) was found to be less than 4% when those from applied to medicinal plants and CPM samples.