Abstract: Glassy Carbon Electrode GCE was modified with different composites to increase the efficiency of analyzing trace Hg2+ by cyclic voltammetry. The structure and composition of the modified GCE was processed using different methods for using Carbon Nanotubes CNT, Activated Carbon AC and C60 on GCE to produce three modified electrodes CNT/GCE, AC/GCE and C60/GCE. The comparison study to choose the best modified electrode for detecting traces of Hg2+ ion by calibration curve. A wide linear range and good repeatability were obtained for Hg2+ detection by CNT/GCE in aqueous 0.1 M KCl as the supporting electrolyte, the relative standard deviation of three modified electrodes are better for CNT/GCE than AC/GCE and C60/GCE. The most modified electrode to detect the trace of Hg (II) in 0.1 M KCl as supporting electrolyte is CNT/GCE.