Abstract: Based on the color reaction between derivatives of serotonin and p-dimethylaminobenzaldehyde (also named as Ehrlich reagent),total amount of serotonin derivatives in extracts of safflower seeds was determined by spectrophotometry.Main influential factors and reaction mechanism of the method were studied.It was found that the mechanism of the color reaction was in compliance with the electrophilic substitution of the indole ring at its 2nd carbon position.Absorption maximum of the colored complex was found at the wavelength of 625 nm,and linear relationship between values of absorbance and concentration of serotonin derivative was found in the range from 0.025-0.5 mmol·L-1.Tests for recovery and precision of the method were made on the base of several samples of extracts of safflower seeds taken from Xinjiang,giving values of recovery in the range of 97.5%-101.7% and values of RSD′s (n=7) less than 2%.