Temperature-dependent direct current (dc) and microwave (mw) conductivity, sigma (dc) and sigma (mw), electron paramagnetic resonance (EPR), and mechanical properties of sulfonated polyaniline/poly(p-phenylene terephthalamide) (SPAN/PPD-T) composite fibers are presented. Tenacity and modulus are in the range of 15 and 270 g/denier (gpd), respectively, for 30 wt % (weight percent prior to sulfonation) SPAN composite fiber. Room-temperature de conductivity sigma (RT) varies from 7.8 x 10(-5) to 1.5 x 10(-1)S/cm, increasing with increasing wt % polyaniline (PAn) and spin stretch factor (SSF). The temperature-dependent conductivity follows the quasi-one-dimensional variable range hopping (Q1D VRH) model: sigma (dc)(T) = sigma (0) exp [-(T-0/T)(gamma)], where gamma similar to 0.5 and sigma (0) is a constant. T-0 is 4.3 x 10(4) to 2.9 x 10(4) K, respectively, for 10 and 30 wt % PAn. The a,, of the fiber with the same SSF 7.0 but a 30/70 PAn/PPD-T ratio shows a typical temperature dependence for materials for which the hopping conduction mechanism is dominant. There is a larger difference between the ad, and a,, following adjustment for the PAn/PPD-T ratio for 10/90 than for 30/70 as expected from lower conductivity. The similar To with different sigma (RT) for samples having the same PAn/PPD-T ratio but different SSF suggests that spin stretching leads to the merging or alignment of the microfibers of SPAN followed by interconnection to each other without significant changes within the individual SPAN microfiber. The densities of Curie spins are similar to 0.055 and 0.0074 spins/2-ring aniline repeat unit, respectively, for 30 and 10 wt %. The density of states at the Fermi level N(E-F) is similar to 0.64 and 0.57 states/eV(.)2-rings, similar to 80% of what would be for PAn in which 50% of the rings are sulfonated, which is consistent with the sulfur analysis. Transport and magnetic data indicate an improved conduction in fiber samples compared with powder samples due to better alignment caused by spin stretching. These results suggest the formation of polarons and a conducting band based on the polaron energy level, consistent with earlier reported experimental results and models for 50% and 75% SPAN.