The analytical performance of the EDTA-CPE sensor that is designed for the detection of metals was studied. EDTA plays an important role in the complexation of metal ions because of their good and high response to these ions. The modified electrode EDTA-CPE was used for the voltammetric determination of mercury ions (square wave voltammetry). Sodium chloride solution 0.3mol−1 was used as the support electrolyte. Using optimal parameters, calibration graph is linear (varying from 5 to 35∗10−4mol/l) for 5min of pre-concentration time with the detection limit of 16, 6×10−9molL−1. These results indicate that the developed method is simple, with high stability and sensitivity for the determination of low concentration of Hg (II). Keywords: Mercury, Voltammetric determination, Modified electrode, Square wave voltammetry