Mixed ion/electron conductive ceramic materials, like perovskite, have recently gained relevance due to their possible applications in membrane technology. This work describes the preparation and characterization of a mixed conductive membrane obtained via in situ polymerization of polyaniline (PANI) within a sulfortated poly(ether ether ketone) (SPEEK) matrix. Mixed conductive membranes of PANI/SPEEK obtained from an initial composition of 80wt.% SPEEK had an electronic conductivity of 1 x 10(-5) S cm(-1) and after a second doping with 1 mol L-1 HCI it increased to 4.9 x 10(-5) S cm(-1). The doping of PANI with SPEEK was evaluated by infrared spectroscopy, with intense broad bands at 1137 and 1157cm(-1). These bands were characteristic of the protonated imine structure of PANI, and also the reduction of quinoid units due to the interaction of the sulfonic groups of SPEEK with nitrogen atoms of PANI. The PANI doping efficiency with SPEEK, the conducting path formation at the percolation threshold and a good thermal stability of the system make it possible to obtain mixed conductive membranes. (c) 2005 Elsevier B.V. All rights reserved.