Proton-conducting polymer composites containing perfluorosulfonic polymer (Nafion) and polypyrrole (PPy) nanoparticles in a polyacrylamide network, P(AAM-MBAM), were synthesized as proton-conducting electrolytes. An investigation into the assembling of Nafion polymer molecules as well as the colloidal PPy-Nafion complexes in the P(AAM-MBAM) network was carried out on the basis of DSC and XRD analysis. It was found that the proton conductivity of the composites was largely affected by the occurrence of the free volume between the P(AAM-MBAM) network and Nafion polymer as well as the concentration of the PPy-Nafion complexes in the composites according to the measurements of the electrical resistance and the frequency-dependent impedance. Copyright 1999 Academic Press.