In this article, by ultrasonic-assisted dispersion of poly(ethylene glycol) (PEG) and multiwalled carbon nanotubes (MWCNTs), methyl methacrylate (MMA) and acrylic acid (AA) are copolymerized and crosslinked through in situ radical bulk polymerization, namely fabricating P(MMA-co-AA)/PEG/MWCNTs composites. The influences of MWCNTs contents in morphology, thermal and mechanical properties of the composites are investigated. After treated by mixed acid, MWCNTs can be uniformly dispersed in P(MMA-co-AA)/PEG due to the hydrogen bonding. Compared with P(MMA-co-AA)/PEG, both the glass transition temperature and the degradation temperature of the composites increase with increasing content, and increase at least 7 and 13 °C, respectively; their tensile strength and impact strength at least increase 9 and 65 %, respectively, and the elongation at break is reduced by at least 8 %.