Blends of polyaniline protonated with functionalized sulfonic acids dopant and various block copolymers of poly (1,4-butylene terephthalate)-co-polytetramethylene oxide having variable proportion of hard to soft segment can be cast as freestanding films from hexafluoro-2-propanol solution. The electrical conductivity of these blends showed percolation threshold values below 1%, a behavior which is indicative of a fibrillar network phase-separated morphology. A significant effect of the counter-ion of the functionalized acid dopant was noted. Polyaniline doped with camphor sulfonic acid or with methane sulfonic acid produced higher conductivity values than polyaniline doped with dodecylbenzene sulfonic acid. The hard segment in the insulating copolymer was found to suppress the electrical conductivity of the resulting compositions. The phase-separated morphology in these blends was confirmed from the observed approximate linear relation of the specific volume on the composition of the blend.