Abstract: In a citric acid-phosphate buffer of pH 3.0,an ion-pair complex was formed between alkaloids in the sample and the color reagent bromophenol blue reacted at 30 ℃ for 5 min.The complex was extracted with CHCl3 in which the absorbance was measured at the wavelength of 413 nm.Pure vindoline (purity:>99%) was used as reference standard in the preparation of calibration curve.Linear relationship between the absorbance and concentration of vindoline was obtained in the range of 0.04-0.28 g·L-1,corresponding to the linear regression equation Y=0.182 4 X-0.03 (r=0.999 3).On the base of a known sample,different amounts of standard solution of vindoline were added separately to 8 portions of the sample solution to test for recovery of the method,the average value of recovery obtained was 99.49%.Total alkaloids in different parts of Catharanthus roseus were determined by the proposed method,giving results of 2.230% (in roots),0.411% (in stems),1.098% (in leaves),0.503% (in flowers) and 0.013% (in seeds).