Functionalized poly(propylene-co-ethylene) (PPE) made via reactive extrusion dramatically improved the performance of their blends with poly(methyl methacrylate) (PMMA). Adhesion, compatibility, modulus, hardness and scratch resistance were all increased for blends with functional PPEs compared to non-modified PPE, greatly expanding the applications of polyolefins. Three types of functional PPEs including maleic anhydride grafted PPE (PPE-MA), hydroxyl group grafted PPE (PPE-OH) and secondary amine group grafted PPE (PPE-NHR) were melt blended with PMMA at different compositions and with PMMA of different molecular weights. Compatibility of each functional PPE with PMMA was compared by investigating the binary blends using mechanical (nano-indentation, nano-scratch and tensile tests), morphological (scanning electron microscopy with image analysis, particle size analysis) and adhesion tests. Compatibility of functional PPEs with PMMA is confirmed consistently from various tests and ranked in a decreasing order as follows: PPE-NHR > PPE-OH > PPE-MA > PPE. We also drastically improved the compatibility and adhesion between PPE and PMMA by blending a small amount of PMMA grafted PPE copolymer.