AbstractIn the present work, in situ polymerizations of sulfonated polyoxadiazole through a polycondensation reaction of A–A (hydrazine sulphate) and B–B (aromatic dicarboxylic acid) monomers with carbon nanotubes in poly(phosphoric acid) were performed. The structures of composites were characterized by elemental analysis, Raman and FTIR spectroscopy. The sulfonated polyoxadiazole composites with high molecular weight (in the order of magnitude of 105 g/mol) are soluble in organic solvents and can be cast as dense films. They exhibit good mechanical properties (storage modulus up to around 4 GPa at 300 °C) and an electrical conductivity in the order of 10−5 S m−1. The composites can be used at temperatures as high as 470 °C.