This invention provides a process for producing an electrode catalyst for a fuel cell, comprising a first support step of producing metallic fine particles having an average particle diameter of 0.1 to 1.5 nm provided at regulated particle intervals on an electroconductive carbon carrier, and a second support step of growing a metal identical to or dissimilar to the metal using the metallic fine particles as a nucleus. In the first support step, the metallic fine particles are supported by an immersion method. The above constitution can provide an electrode catalyst for a fuel cell, which has a high level of percentage support, has a high level of dispersibility, and has improved methanol oxidation activity per weight of the catalyst. Further, when treatment in an atmosphere containing hydrogen is carried out at a low temperature below 100° C., the methanol oxidation activity per active surface area can be improved without lowering the active area.