Abstract: A catalytic and sensitive spectrophotometric method for the determination of diethylstilbestrol （DES）with CTMAB has been developed. The method is based on the phase transfer catalysis and sensitive complex ation characteristic of CTMAB. The study showed that Fe（Ⅲ）was reduced to Fe（Ⅱ）by DES and a stable multi-micelle complex was formed by Fe（Ⅱ）and K₃［Fe（CN）₆ ］in the existence of CTMAB，the maximum absorption is at at 736 nm. Lambert-Beer law was well obeyed at DES concentrations ranging from 0. 032 56 to 0. 652 1 μg/mL，regression equation was A = 0. 002 7+0. 399 0 ρ，correlation coefficient R² was 0. 999 1，detection limit was 1. 35 μg/mL and the molar absorption coefficient was ε = 5. 43 × 105（L·mol^-1·cm^-1）；the relative standard deviation was 0. 89%. The proposed method was used in the determination of DES in powdered milk and the recovery was 89.3% ～ 101.6%.

Key words: diethylstilbestrol（DES）, visible spectrophotometry, CTMAB