High-temperature proton exchange membrane fuel cells (HT-PEMFCs) utilize a phosphoric acid- (PA-) doped polybenzimidazole (PBI) membrane as a polymer electrolyte. The PA concentration in the membrane can affect fuel cell performance, as a significant amount of PA can leak from the membrane electrode assembly (MEA) by dissolution in discharged water, which is a byproduct of cell operation. Spectrophotometric analysis of PA leakage in PA-doped polybenzimidazole membrane fuel cells is described here. This spectrophotometric analysis is based on measurement of absorption of an ion pair formed by phosphomolybdic anions and the cationoid color reagent. Different color reagents were tested based on PA detection sensitivity, stability of the formed color, and accuracy with respect to the amount of PA measured. This method allows for nondestructive analysis and monitoring of PA leakage during HT-PEMFCs operation.