A novel kind of potentiometric sensor for the determination of risedronate in pharmaceutical products is proposed. This potentiometric sensor is comprised of a poly(vinyl chloride) (PVC) membrane based on an anion-exchanger, tridodecylmethylammonium chloride (TDDMACl), and coated with a polyaniline (PANI) layer. The potentiometric response towards a highly hydrated risedronate species was strongly promoted by the presence of the PANI layer. In contrast to uncoated membranes, the PANI-coated membrane exhibited a sensitivity of −39.9 ± 0.9 mV decade⁻¹ and the detection limit reached 0.45 mg mL⁻¹. The results of the potentiometric analysis of risedronate agreed with those obtained with a validated chromatographic method. The TDDMACl-based membrane coated with the PANI layer differentiated 0.94 wt % and 3.44 wt % of a specific contaminant in 1.6 mg mL⁻¹ risedronate.