Poly[2,2'-(p-oxydiphenylene)-5,5'-bibenzimidazole] (OPBI) nanocomposites containing 0.1-1 wt% multi wall carbon nanotubes (MWNTs) have been synthesized via "one pot synthesis" which combines the in situ modification of MWNTs and in situ polymerization of OPBI in one reaction pot, a technique that is particularly suitable for large scale production. Raman spectroscopy, NMR, XPS and XRD characterizations of OPBI grafted MWNTs (MWNT-g-OPBI), purified from the MWNT-g-OPBI/OPBI hybrid, reveal that the OPBI chains are successfully attached to the surface of MWNTs in the process of one pot synthesis method. Fracture morphology of the nanocomposites reveals very efficient distribution of the MWNTs within the OPBI matrix with good interfacial interaction. The mechanical properties (including tensile and yield strength, Young's modulus, etc.) are obviously increased even at 0.1 wt% MWNTs loading, and further improvement is observed at higher filler contents. The thermal stability and electrical conductivity are also improved with the incorporation of MWNTs. (C) 2009 Elsevier Ltd. All rights reserved.