An electrode catalyst and a method for producing the electrode catalyst are described, in which the electrode catalyst includes catalyst metal particles containing platinum or a platinum alloy, and carrier particles supporting the catalyst metal particles. The carrier particles are made of a carbonaceous material with a BET specific surface area of 700 m2/g or more. The catalyst metal particles have an average particle size of 2.5 to 4.5 nm, and a standard deviation of the particle size of the catalyst metal particles is 1.30 nm or less. The electrode catalyst has a high initial activity and is able to maintain that activity over a long period of time.