A nanocomposite carbon composed with single wall carbon nanotube (SWNT) and nanoporous carbon (NPC) was prepared by grafting a carbonizable polymer, poly(furfuryl alcohol) (PFA) to a SWNT. The SWNT was first functionalized with arylsulfonic acid groups on sidewall (SA-SWNT) and then converted to PFA-functionalized SWNT (PFA-SWNT) by in situ polymerization of furfuryl alcohol (FA). NPC/SWNT nanocomposite carbon was generated by heating PFA-SWNT in argon at 600°C A continuous phase was formed between SWNT and NPC. The deformation of the nanocomposite carbon at high temperature was studied by heating it at temperatures from 1200 to 2000°C and characterized with HRTEM and Raman spectra. It was found that NPC tended to graphitize along the axis of neighboring nanotubes at temperature higher than 1400°C Complete graphitization of NPC and SWNTs was obtained at 2000°C, when the NPC transformed to graphitic nanoribbon (GNR) and SWNT or DWNT collapsed within the confines of the GNR. Nanocomposite polymer and carbon fibers were prepared by dispersing small amount of SA-SWNT in FA, followed with polymerization, thermosetting and pyrolysis. The composite polymer fibers' Young's modulus was lower than the pure PFA fibers prepared at the same conditions. However, after heated in argon at 300°C, 400°C, 500°C and 600°C respectively, the Young's modulus of the nanocomposite carbon fibers turned to be higher than the fibers derived from pure PFA with treating temperature higher than 400°C. The average Young's moduli enhancement is ∼13% with only 0.1wt% of SA-SWNT in FA.