A new PVC membrane, ion selective electrode (sensor) was constructed and used for the determination of Escitalopram oxalate (ESC) in pure form and pharmaceutical preparation; the electrode was based on the use of the ion association complex of sodium tetra phenyl borate (STPB) as an anion with ESC as a cation in polyvinyl chloride (PVC) matrix with tri-butyl phthalate (TBPH) as a plasticizer. The results of this electrode showed stability (lifetime 30 days), near a Nernstian slope of 55.9 mv/decade, over a concentration range from 1x10-1-1×10-5 M, the electrode was found to be usable within the pH-range 3.0 – 6.0. This study also encompassed the measurements of the selectivity of this electrode in the existence of common cations, anions, and some drug excipients, and the selectivity factor was less than 1.0. The electrode was successfully applied to determine ESC in pharmaceutical preparation with a recovery of no less than 98.87%.