In the present paper, the effects of reactive copolymer containing maleic anhydride on the thermomechanical properties of poly(methyl metacrylate) (PMMA) were investigated. Maleic anhydride-styrene (MA-St) and aniline maleamidic acid-styrene copolymers (AnMAA-St) were used as reactive copolymers. Multicomponent blends such as PMMA/MA-St/AnMAA-St were prepared and thermomechanical characterisation of these blends was performed by thermomechanical analysis method (TMA). The blends were prepared by changes of the weight ratios of MA-St and AnMAA-St copolymers in the blends. PMMA contents in all the blends are fixed at a weight of 75%. Consequently, it is clear that MA-St copolymer can be used for changes of the thermomechanical properties of PMMA.