The effect of an organic solvent contained in a catalyst ink on the catalyst layer structure was revealed by measuring the porosity and thickness of catalyst layers in the decal method to fabricate membrane electrode assemblies (MEAs) in polymer electrolyte membrane fuel cells. In this study, ethylene glycol and propylene glycol were used as organic solvents. The pore volume of the catalyst layer fabricated from a catalyst ink containing ethylene glycol (CLEG) was smaller than that containing propylene glycol (CLPG) near the peak pore diameter of 54-66 nm, suggesting the intrusion of perfluorosulfonate-ionomer into the space between carbon black-supported platinum (Pt-C) particles could reduce the pore volume and extend the active reaction area of CLEG compared with CLPG. The thickness of CLPG was 1.3 times larger than that of CLEG at a fixed platinum loading, m(Pt), suggesting mass transport could restrict the cell performance of CLEG compared with CLPG. The expectations from these two structural analyses were verified by measuring the cyclic voltammograms and current density vs voltage (i-V) curves of a single cell for MEAs fabricated from catalyst inks containing either ethylene glycol or propylene glycol with various m(Pt).