Disclosed is an oxide and/or nitride support for electrode catalysts, which is used for electrodes for polymer electrolyte fuel cells (PEFC). The support for electrode catalysts is an aggregation body of primary particles of oxide of at least one kind of metal selected from rare earths, alkaline earths, transition metals, niobium, bismuth, tin, antimony, zirconium, molybdenum, indium, tantalum, and tungsten, and the aggregation body is configured such that at least 80% of the metal oxide primary particles having a size of 5 nm to 100 nm aggregate and bind each other to form dendritic or chain structures each of which is made of 5 or more of the metal oxide primary particles.