An oxidizer catalyst assembly for use in a fuel cell system for oxidizing anode exhaust gas and in which a first catalyst member is situated along a gas flow path and a second catalyst member is situated along the gas flow path following the first catalyst member. Each of the catalyst members includes a plurality of channels for passing the gas therethrough and an oxidizing catalyst deposited in the channels. The channel density of the channels of the second catalyst member is greater than the channel density of the channels of the first catalyst member and the channel width of the channels of the second catalyst member is less than the channel width of the channels of the first catalyst member.