Multi-walled carbon nanotubes (MWCNTs) were introduced into polyimide matrix to fabricate high temperature microwave absorbing materials. The flexural strength can reach 125 MPa with 2 wt% MWCNTs, and the flexural strength decreases with increasing the filler content due to the filler reinforcement. The complex permittivity of the nanocomposite increases with increasing the temperature owing to shorten the relaxation time and enhance the electrical conductivity at elevated temperature. When the content of absorbent is 5%, the -10 dB absorption bandwidth could reach 1.3 GHz, with the thickness of 2.1 mm, while the bandwidth below -10 dB is 2.04 GHz with the thickness of 1.7 mm at 373 K. (C) 2015 Elsevier B.V. All rights reserved.