Poly(methyl methacrylate) (PMMA) was grafted onto multiwalled carbon nanotubes (MWNTs). Composites of PMMA-grafted MWNTs and poly(styrene-co-acrylonitrile) (SAN) were prepared by solution casting from tetrahydrofuran. Since PMMA is miscible with SAN, the two polymers mix intimately to facilitate the dispersion of PMMA-grafted MWNTs in the SAN matrix. The intimate mixing is evidenced by the transparency of the composites. The incorporation of PMMA-grafted MWNTs to SAN (effective MWNT content = 0.5-2 wt%) leads to increases in storage modulus at 40 degrees C, Young's modulus, tensile strength, ultimate strain, and toughness by 90, 51, 99 184 and 614%, respectively. Such simultaneous increases in stiffness, strength, ductility and toughness of a polymer by rigid fillers are rarely observed. (c) 2005 Elsevier Ltd. All rights reserved.