In this study, the Taguchi method was applied to determine optimum working conditions in obtaining maximum power density of a PEMFC. Performance measure analysis was also followed by performing a variance analysis, in order to determine the optimum levels and relative magnitude of the effect of parameters. The optimum working conditions were found to be system pressure, 5 bar; flow rate ratio of H-2 and O-2, 1/2; temperature of fuel cell, 75 degrees C and temperature of humidifiers, 75 degrees C. Under these conditions, the amount of maximum power density was predicted as 353 mW cm(-2) by using experimental results obtained according to Taguchi's orthogonal array (OA) L-9(34). Verification experiment was done for the same optimum conditions and maximum power density was observed as 379.64mWcm(-2). According to the results of this optimization, it was seen that pressure and humidification temperature were the effective parameters. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.