A direct electroanalytical method for the determination of estrogens is proposed, and a carbon paste electrode modified with oleic acid for the electrochemical oxidation of estrogens is described. A sensitive and reproducible peak is obtained by comparison with voltammetric responses at different modified electrodes (CPA, CPOSaand CPOPa). The experimental parameters and electrochemical properties of estrogens at the modified electrodes are discussed. Its oxidation current depends on the electrolyte species and the alcohol content. The carbon paste electrodes modified with oleic acid have been developed for the assay of estriol in pharmaceutical samples. A detection limit 4 × 10−7mol/l of estradiol is estimated under selected conditions by using the 1.5th order differential stripping analysis.