Poly(ether ketone) (PER) was grafted onto few wall carbon nanotube (FWNT) using in-situ polymerization of 4-phenoxybenzoic acid (4-PBA) in poly(phosphoric acid) (PPA), and fibers were processed using dry-jet wet-spinning. The PEK/FWNT weight ratio was in the range of 99/1 to 80/20. The fibers have been characterized for their morphology, structure, mechanical properties, as well as electrical conductivity. The toughness (work of rupture) of the PER fibers, as measured from the area under the stress strain curves, was as high as 130 J/g and often exceeded the toughness of the toughest synthetic fibers such as Kevlar (TM) (similar to 45 J/g) and Zylon (TM) (similar to 50 J/g) and approached values closer to that of spider silk (similar to 170 J/g). PEK and PEK-g-FWNT fibers exhibit good thermal stability with degradation onset of above 500 degrees C under nitrogen environment, and possess high char yield (similar to 50% for 5 wt% FWNT containing PEK fiber). PEK-g-FWNT fibers can be processed that exhibit good dimensional stability up to 300 degrees C (coefficient of thermal expansion similar to-1.2 x 10(-5)/degrees C) and the axial electrical conductivity was as high as 240 S/m at 20 wt% FWNT loading. (C) 2010 Elsevier Ltd. All rights reserved.