In an aspect of the invention, a fuel cell electrocatalyst comprises a carrier and a catalyst layer made of a Pt—Ru alloy supported on the carrier, and having the oxygen content of 4.4 wt % or less. Moreover, a value of the amount of oxygen that exists in one layer of the outermost surface of a component atom of the catalyst layer is 14.1% or less. Furthermore, in another aspect of the invention, a method of producing the fuel cell electrocatalyst comprises a supporting step of supporting a catalyst layer made of an alloy including Pt and Ru on a carrier, and an oxygen content regulating step of regulating the oxygen content of the catalyst layer.