The present invention relates to an oxygen reduction catalyst, an electrode, a membrane electrode assembly, and a fuel cell, and the oxygen reduction catalyst is an oxygen reduction catalyst containing substituted CoS2, in which the substituted CoS2 has a cubic crystal structure, the oxygen reduction catalyst contains the substituted CoS2 within 0.83 nm from the surface thereof, and the substituted CoS2 has at least one substitutional atom selected from the group consisting of Cr, Mo, Mn, Tc, Re, Rh, Cu, and Ag in some of Co atom sites.