Ion selective electrode (ISE) is an electrode that has been designed to identify heavy metal ion in a solution. In this experiment, thiazole-4-carboxamide (Th) is used as ionophore and sodium tetraphenylborate (NaTPB) as an additive. Polyvinyl chloride (PVC) was used as a polymeric matrix in the membrane selective electrode. Different type of commonly used plasticizers is analysed to choose the one with the best response. There are four types of plasticizer used; dioctyl phthalate (DOP), dibutyl phthalate (DBP), benzyl acetate (BA) and nitrobenzene (NB). The ratio (w/w)% used for all plasticizers Th:PVC:NaTPB:Plasticizer is 5.0:30.0:2.0:63.0. ISE is used in a sample solution with different concentration to figure out the best plasticizer. Ion selective membrane using BA gives the best response with 19.3�1.4 slope value, while ion selective membrane using DOP gives the least response with 11.3�0.7 slope value.