Polyolefin elastomer-grafted multiwalled carbon nanotubes (POE-MWCNTs) were incorporated in a polyimide (PI) matrix. The POE shell formed on the MWCNTs improved the dispersion of MWCNTs and enhanced the interfacial adhesion between the PI matrix and MWCNTs, leading to improvements in storage modulus and the glass transition temperature of the composites and enhancement of the electrical properties of PI. Thus, composites with 4–5 wt% POE-MWCNTs showed increased electrical properties by about 60–70% and retained the high impact strength when compared with the neat PI.