All-organic polyaniline (PANI)/sulfonated poly(aryl ether ketone) (SPAEK) composite membranes consisting of a PANI (conducting) filler evenly distributed in an SPAEK (insulating) matrix were prepared with a solution-blending technique. The dielectric properties, electrical conductivity, and thermal and mechanical performances of the all-organic PANI/SPAEK composite membranes were investigated as a function of different PANI loading levels. The composite membrane containing 30 wt % PANI exhibited a high dielectric constant of about 600, a low dielectric loss tangent of about 0.6 (at 1 kHz), and good thermal properties (temperature for 5% weight loss>250 degrees C) and mechanical properties (tensile strength approximate to 35 MPa). (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1990-1995, 2013