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-stryrenemethyl 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.