The in situ polymerization and crosslinking of sodium salt of sulfonated styrene in the pores of nation 117 membrane has been studied for the evaluation of electrical performance of the resultant semi-IPN (semi -interpenetrating polymer network) membrane in direct methanol fuel cell (DMFC). The formation of semi-IPN is confirmed from the presence of aromatic characteristics peak in the FTIR spectra. Impedance results indicate that the semi-IPN sample with higher water uptake exhibits lower interfacial resistance compared to a sample with water uptake. This indicates that the semi-IPN formed in the pores of nation 117 membrane has the ability to reduce methanol crossover by blocking the transportation. At higher temperatures (> 110 degrees C and lower current density (< 25 mA cm(-2)), the electrical performance (power density) of a DMFC with a representative semi-IPN sample is observed to be higher than that with a nation membrane. (C) 2006 Elsevier B.V. All rights reserved.