We studied the effect of blending styrene-methyl methacrylate-maleic anhydride copolymer (SMA) on rheology and foaming of poly(methyl metacrylate) (PMMA). The blends are transparent over a wide range of blending ratio and can be miscible. Although the blends showed a slight increase of storage modulus in low frequency region at the molten state, the apparent change in non-linear viscoelasticity was not observed. At the identical carbon dioxide adsorbed amount, the blends showed very unusual foaming behaviors depending on the blend ratio.