Polyacrylonitrile (PAN)/single wall carbon nanotube (SWNT) composite films have been processed with unique combination of tensile strength (103 MPa), modulus (10.9 GPa), electrical conductivity (1.5 X 10(4) S/m), dimensional stability (coefficient of thermal expansion 1.7 X 10(-6)/degrees C), low density (1.08 g/cm(3)), Solvent resistance, and thermal stability. PAN molecular motion above the glass transition temperature (T-g) in the composite film is significantly suppressed, resulting in high PAN/SWNT storage modulus above T-g (40 times the PAN storage modulus). Rope diameter in the SWNT powder was 26 nm, while in 60/40 PAN/SWNT film, the rope diameter was 40 nm. PAN crystallite size from (110) plane in PAN and PAN/SWNT films was 5.3 and 2.9 nm, respectively. This study suggests good interaction between PAN and SWNT. (c) 2005 Elsevier Ltd. All rights reserved.