Abstract Surfactant has been successfully applied to enhance the dispersion of carbon nanotubes (CNTs) in polymer and the properties of nanocomposite. CNTs were treated with a nonionic surfactant Triton X-100, and its effects on dispersion state, surface chemistry, structure and morphology of CNTs, as well as on the thermomechanical, mechanical and electrical properties of CNT/epoxy nanocomposites were evaluated. The mechanical properties such as impact fracture toughness, flexural strength and modulus, the thermomechanical properties, as well as the electrical conductivity of the nanocomposite all showed significant improvements after the treatment. The above observations are attributed to the “bridging” effects between the CNT and epoxy, which are introduced by the hydrophobic and hydrophilic segments of the nonionic surfactant. The enhanced interfacial interactions gave rise to improved dispersion and wetting of CNTs in polymer matrix, enhancing the mechanical and fracture properties of the nanocomposite. Unlike chemical functionalization techniques, however, the surfactant treatment exhibited little adverse effect on electrical conducting behavior of the nanocomposite.