Operation tests were applied to fuel cell with perfluorosulfonic acid (PFSA) polymer for membranes and electrodes. Degradation of PFSA polymer in catalyst layers after the tests was investigated using F-19 NMR. As the decomposition products, six kinds of the side-chain fragments were acquired from the water and the methanol extracts, and the each weight of the fragment was acquired. The side-chain fragments indicate that side-chain scission occurs at two positions in the side-chain. Moreover, reduction of relative equivalent weight for all PFSA polymer (EW*all) and amounts of PFSA polymer in catalyst layer after the tests suggests that main-chain scission occurs. Hydrogen peroxide vapor (HPV) exposure tests were applied to PFSA polymer membranes. PFSA polymer degradation after the tests was investigated using ion chromatography and total organic carbon analysis for trap water, and using (FNMR)-F-19 for water/methanol extracts of membranes. Decomposition products other than fluoride ion accounted for a significant portion of degradation weight loss, and their generation rates were not proportional to fluoride.ion release rate (FRR). The differences between the results of FRR and other decomposition product analysis strongly suggest the presence of two or more decomposition mechanisms in PFSA degradation. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.076304jes] All rights reserved.