In the present paper, the effects of reactive terpolymer containing maleic anhydride on the thermomechanical properties of PVC were investigated. The thermomechanical behaviour of multicomponent blend based on poly( vinyl chloride) ( PVC), PVC/maleic anhydride-stryrene methyl metacrylate ( MA-St-MMA)/n-pentyl maleat-styrene-methyl metacrylate( nPnMA-St-MMA) were studied using the TMA method. The blends were prepared by changing the weight ratio of MA-St-MMA and nPnMA-St-MMA terpolymers, and keeping the PVC content fixed at 75 wt-%. The MA-St-MMA terpolymer, a reactive copolymer, formed the compatible blends with PVC. Results indicated that the elastic properties of PVC could be controlled by the MA-St-MMA terpolymer.