The PVC membrane immobilized with lansoprazole-tungstate and plasticized with dioctyl phthalate was characterized by FTIR, XRD, and SEM. The effects of critical parameters such as response time, pH, and temperature on the potential were analyzed, and these were optimized using central composite design (CCD) and desirability function. Under the optimized conditions, the plot of measured potential against concentration of lansoprazole exhibited linearity from 2 X 10(-5) to 2 X 10(-3) mol L-1 at pH 4.4. The slope of the plot and detection limit was -41.50 mV/decade and 1.57 X 10(-5) mol L-1, respectively. The response time of the proposed ionselective electrode was <= 30 s. The electrode exhibited good selectivity for lansoprazole over a number of ionic species, commonly found in commercial dosage forms. The response mechanism was also discussed. The proposed ion-selective electrode was successfully applied for potentiometric determination of lansoprazole.