A new electrochemical micro-sensor has been designed for the sensitive detection of ultra-traces of 17α – ethinylestradiol (EE2). A carbon paste cavity micro-electrode modified by carbon black nanoparticles (GC-nCB)-µCPE was used with an electrochemical preconcentration (EP) step of EE2 on (GC-nCB)-µCPE at 0.0 V during 300 s in a 0.01 mol.L-1 phosphate buffer solution (pH = 7.4) before voltammetric determination. The results demonstrate that two line calibrations were obtained in the concentration ranges of 0.005 to 0.2 μmol.L-1 and 0.2 to 1 μmol.L-1. The detection and quantification limits are estimated at 1.4 nmol.L-1 and 4.9 nmol.L-1, respectively. Moreover, a high sensitivity of 4.16 µA.mol−1.L and good selectivity for the quantification of EE2 in the presence of different interfering organic and inorganic compounds were observed. Based on the results (satisfactory recovery (less than 3.5 %) and relationship standard deviation (less than 2.5 %)), the designed micro-sensor can be successfully applied to the analysis of EE2 in environmental water samples and in biologic fluids. The modified microsensor presented an efficient and inexpensive tool for the quantification of EE2.