A novel microemulsion based on sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was developed for the simultaneous determination of natural and synthetic estrogens by microemulsion EKC (MEEKC). The microemulsion system consisted of 1.4% w/w AOT, 1.0% w/w octane, 7.0% w/w 1-butanol and 90.6% w/w 20 mM sodium salt of 3-(cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO) and 10 mM phosphate buffer at pH 12.5. A baseline resolution in the separation of estrone, 17 beta-estradiol, estriol, estradiol 17-hemisuccinate, etinilestradiol, estradiol 3-benzoate, and estradiol 17-valerate was achieved in comparison to the traditional MEEKC system with SIDS in less than 15 min. The optimized electrophoretic conditions included the use of an uncoated-silica capillary of 60 cm of total length and 75 mu m id, an applied voltage of 25 W, a temperature of 25 degrees C and 214 UV-detection. Parameters of validation such as specificity, linearity, accuracy, LOD, LOQ and robustness were evaluated according to international guidelines. Due to its simplicity, accuracy, and reliability, the proposed method can be an advantageous alternative to the traditional methodologies for the analysis of natural and synthetic estrogens in different pharmaceutical forms.