Adsorptive stripping voltammetry using a glassy carbon electrode modified by a film of aminosepiolite was utilized for simultaneous pre-concentration and trace detection of cadmium, lead, and mercury ions in aqueous solution. The modified sepiolite exploited as electrode material was obtained by grafting on its surface of [(3-(2-aminoethylamino)propyl)]trimethoxysilane (AEPTMS). The results demonstrated that the amine groups on sepiolite efficiently affected the voltammetric detection of heavy metals. The full factorial design matrix and response surface methodology were applied in designing experiments, to determine the optimal conditions and to evaluate their mutual interactions. The high values of adjusted R2 obtained of the fitted model show that the experiments data were well explained by the model, which then allowed to acquire optimum parameters for the electroanalysis and detection of the analytes by differential pulse voltammetry. At pH 6.5 of accumulating medium, with an electrolysis potential of –0.9 V and in the concentration range of 10−8 M to 10−9 M, calibration plots were obtained. The limits of detection (3Sd/m) were 8.689 × 10−10 M, 8.197 × 10−10 M, and 8.099 × 10−10 M, respectively, for Cd2+, Pb2+, and Hg2+ ions. The interference effect of several cations and anions on the response of the analytes was also evaluated, and finally, the sensor was applied to the simultaneous detection of metal ions in tap water with satisfactory recovery rates.