Conducting copolymer poly(aniline-co-p-phenylenediamine) [poly(Ani-co-pPD)] and surface-modified magnetite (Fe3O4) composites were synthesized by ultrasonically-assisted chemical oxidative polymerization. Fe3O4 nanoparticles were surface-modified with silane coupling agent methacryloxypropyl-trimethoxysilane (MPTMS) in order that they would be well dispersed for the reaction process. It was also found that the aggregation of Fe3O4 nanoparticles could be reduced under ultrasonic irradiation. TEM analysis confirmed that the resulting poly(Ani-co-pPD)/Fe3O4 nanocomposite showed core-shell morphology, in which Fe3O4 nanoparticles were well dispersed. The incorporation of Fe3O4 in the nanocomposites was endorsed by FT-IR. The nanocomposites were also confirmed by UV-visible, TGA and XRD. Conductivity of the nanocomposites was found to be in the range of 7.02 x 10(-4)-6.54 x 10(-6) S/cm. Higher saturated magnetization of 12 emu/g was observed for composite with 20% Fe3O4. (C) Koninklijke Brill NV, Leiden, 2011