An electrode catalyst layer characterized by comprising composite particles comprising electrode catalyst particles supported on electrically conductive particles, a perfluorocarbonsulfonic acid resin (component A) and a polyazole compound (component B), the content of the composite particles being 20 to 95% by weight, the total weight of component A and component B being 5 to 80% by weight, the weight ratio between component A and component B (A/B) being 1 to 999.