A fuel cell stack includes a membrane electrode assembly including a cathode and an anode which are catalyst layers and are formed on a first and a second surface, respectively, of an electrolyte membrane, a first separator disposed at one side of the membrane electrode assembly, and a second separator disposed at the other side of the membrane electrode assembly, wherein a gas path through which a gas is discharged from the cathode or the anode, or a gas is supplied to the cathode or the anode, is disposed between the second separator and the membrane electrode assembly and is formed in a non-reaction zone, and wherein the gas path includes a flow path expansion portion and a height of the flow path expansion portion is greater than a height of a reaction zone.