A polymer electrolyte fuel cell power generation system is disclosed which comprises: a fuel cell having a plurality of cells each having a polymer electrolyte membrane and an anode and cathode that are formed so as to sandwich the polymer electrolyte membrane therebetween, a fuel gas path formed so as to guide fuel gas from an inlet of the fuel gas to the anode of each cell and discharge the fuel gas to the outside therefrom, an oxidizing gas path formed so as to guide oxidizing gas from an inlet of the oxidizing gas to the cathode of each cell and discharge the oxidizing gas to the outside therefrom, and a cooling fluid path formed so as to guide a cooling fluid from an inlet of the cooling fluid to a cooling fluid supply manifold and then to a region opposite to power generation regions constituted by the anodes and cathodes of the plurality of cells and discharge the cooling fluid to the outside therefrom through an outlet of the cooling fluid, the fuel cell being configured to generate electric power accompanied with heat generation by a reaction between the fuel gas and the oxidizing gas within the power generation regions; a fuel gas supply apparatus for feeding the fuel gas to the inlet of the fuel gas of the fuel cell; an oxidizing gas supply apparatus for feeding the oxidizing gas to the inlet of the oxidizing gas of the fuel cell; a cooling fluid supply system for causing the cooling fluid to flow through the cooling fluid path of the fuel cell, thereby cooling the fuel cell; and a control unit, wherein the control unit controls, during the power generation, the temperature of the cooling fluid at the inlet of the cooling fluid 401 though the cooling fluid supply system so as to satisfy T1.gtoreq.T2+1.degree. C. where T1 is a corresponding dew-point temperature of at least either the fuel gas or oxidizing gas at the inlet thereof and T2 is the temperature of the cooling fluid at the inlet of the cooling fluid 401.