Abstract: Diethylstilbestrol (DES) and Dienestrol (DI) are synthetic estrogen and as a growth promoter in meat-producing animals and fowl. Because of the carcinogenic potential of DES and DI, their residues are not allowed in food. The method described here for the determination of DES and DI is based on the selected ion monitoring technique. This method provides a high sensitivity of detection with high specificity.The detection limit of the method was shown to be 0.5ng either for DES or DI. It is suitable for the determination of trace DES or DI in chicken samples as a confirmation method.