AbstractDegradation phenomena of electrocatalysts for proton‐exchange membrane fuel cells and their mechanisms are reviewed. Platinum dissolution and redeposition, carbon‐support corrosion, inhomogeneity during start‐up and cell reversal are discussed as factors that influence the degradation of electrocatalysts with relation to electrode potential. Early research findings at the National Institute of Advanced Industrial Science and Technology (AIST), Japan, are mainly used as a basis of discussion. The development of highly durable electrocatalysts using an oxide support based on the results of degradation studies to suppress electrocatalyst degradation is summarized with a main focus on Pt‐deposited Ti4O7 catalysts developed at AIST. The development of high‐CO‐concentration durable anode electrocatalysts is also reviewed. In particular, an electrocatalyst that uses an organic complex as a co‐electrocatalyst with a platinum ruthenium alloy anode electrocatalyst developed at AIST is included as a novel high‐CO‐concentration durable anode electrocatalyst.