This paper describes polystyrene-block-polyisoprene-block-poly (butyl acrylate) (PS-b-Pl-b-PBA) triblock copolymer that has been prepared by using styrene, isoprene and butyl acrylate monomer. Polymerization involved was an anionic living polymerization reaction using n-butyllithium (n-bub) as an initiator to form polystyrilithium anions by which the reaction showed changes in colour from colourless to reddish orange. The living polymerization was carried out using 5-neck reaction flask equipped with mechanical stirrer, nitrogen gas inlet and thermometer to control polymerization temperature. The synthesized triblock copolymer was collected by precipitation of the mixture in methanol. FTIR indicates the presence of the monomers in the triblock copolymer. The thermal analysis of the PS-b-Pl-b-PBA triblock copolymer have been reported in this synthesis which resulting in low Tg due to the presence of isoprene monomer.