The effect of organic solvents in catalyst inks on the pore structure of catalyst layers (CLs) in polymer electrolyte membrane fuel cells was investigated. The pore size distribution of CLs fabricated from catalyst inks containing either ethylene glycol (EG) (CLEG), propylene glycol (PG) (CLPG), or 1,3-propanediol (PDO) (CLPDO) was measured. The dielectric constants of these three organic solvents were >10, and perfluorosulfonate ionomer was dissolved in the catalyst inks. The pore volume (v) of CLPDO, CLEG, and CLPG increased in this order: v(PDO) < v(EG) < v(PG), suggesting that the pore structure of the CLs depended on the solvent evaporation process. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3439617] All rights reserved.