A sulfate-selective PVC-membrane sensor based on nickel complex of 3, 8-dimethyl 5, 6-benzo- 4, 7-diazadece-3, 7-diene-2, 9-dione (dioxime) as  (a novel sensing material) is presented. The Potentiometric behavior of the sensor was independent on the pH of the solution between 4.5 and 7.5 pH. The sensor revealed a linear response towards SO₄²⁻ ion in the range of 5.0×10⁻⁷to 1.0×10⁻² M with an anionic slope of -30±0.2 mV per decade. The sensor possesses a satisfactory reproducibility, fast response time, low limit of detection (3×10⁻⁷M).The interference of hydrophobic inorganic anions was very low in comparison with the conventional ion-exchanger based electrodes, as shown by the selectivity coefficients determined by the separate solution method (SSM). The selectivity was also good towards the most common univalent and divalent anions. The sensor was used as an indicator electrode in potentiometric titration of sulfate with barium ions and in determination of sulfate in some pharmaceutical products .