The highly selective and sensitive PVC based membrane sensor was fabricated by using 1,3,5-tris [(2,3-dihydroxybenzylamino) amino methyl]cyclohexane (L) as a neutral membrane carrier for the potentiometric determination of Promethazine HCl. The membrane with the composition of33% PVC, 64% Plasticizer, 3% PM-PMD (Ionophore) and 1% NaTPB was found to be best in terms of response characteristics of sensor assembly. The proposed membrane sensor has very low detection limit of 2.0 x 10-8 M, within the concentration range of 5.0 x 10-8 – 1.0 x 10-2 M, and has fast response time of about 10s. The proposed sensor was used for the selective determination of Promethazine HCl. in different synthetic as well as real sample.