TECHNOLOGY FOCUS - POLYMERS - Preferred Process : In the step for increasing the viscosity, the dispersion is subjected to ultrasonic vibration by which the energy given to the dispersion is 0.01 - 10 kWh per 1 kg of the dispersion. In the step for increasing the viscosity, a shear force is applied to the dispersion at a shear rate of 102 - 108 (1/s) by which the energy given to the dispersion is 10 3 - 108 J per 1 kg of the dispersion. The process contains a step for filtering the dispersion to remove rough particles before the step for increasing the viscosity. The process also contains a step for concentrating the dispersion to 3 - 40 wt% of the original wt before the step for increasing the viscosity. The process for producing a thickened ion-exchange polymer dispersion comprises preparing an ion-exchange dispersion by dispersing an ion-exchange polymer comprising a fluoropolymer having sulfone groups so as to obtain an ion-exchange polymer dispersion comprising a dispersion medium and an evenly dispersed ion-exchange polymer, filtering the dispersion, concentrating the dispersion and increasing the viscosity of the dispersion, the steps being carried out in this order. The viscosities, measured at 25 degreesC and at a shear rate of 10 (1/s), of dispersion (A) immediately before the thickening and of the thickened dispersion (B) are 50 - 10000 mPa.s and 1000 - 100000 mPa.s, respectively. The wt of thickened dispersion (B) is 3 - 40 % of that of dispersion (A). The F-containing polymer is a copolymer containing a unit derived from tetrafluoroethylene and a unit derived from CF2=CF(OCF2CFX)m-Op-(CF2)nSO3H.X = F atom or trifluoromethyl group ;m = 0, 1, 2 or 3 ;n = integer = 0 - 12 ;p = 0 or 1In this general formula, when n is 0, p is 0.Preferred Electrode : The process for producing the united film electrode assembly for use in solid polymer-type fuel cells comprises producing a thickened ion-exchange polymer dispersion (B) by the above process, preparing a coating liquid containing a catalyst powder comprising a metal particle catalyst carried on carbon and dispersion (B), coating the coating liquid on a substrate so as to form a layer, and placing the layer, as at least one catalytic layer, in adjacent to a polymer electrolysis film. WIDER DISCLOSURE - A thickened ion-exchange polymer dispersion obtained by this process has a viscosity measured at 25 degreesC and at a shear rate of 10 (1/s), of 1000 - 100000 mPa.s. A process for producing a united film electrode assembly for use for either the anode or the cathode in a solid polymer-type fuel cell (SPFC) contains the invented process for producing a thickened ion-exchange polymer dispersion.    EXAMPLE - A copolymer powder (5000 g) containing a unit derived from tetrafluoroethylene and a unit derived from CF2=CFOCF2CF(CF3)-O- (CF2)2SO3H was hydrolyzed in a mixture solution comprising a 10 % KOH solution (20000 g) and methanol (5000 g) and the resulting products were reacted with 1.5 mol/liter H2SO4 (20 liter) at RT for 0.5 hours so as to obtain a polymer having sulfone groups. The polymer (3000 g) was dispersed in C2H5OH (27000 g) and the mixture was stirred at 80 degreesC for 16 hours. The dispersion was filtered so as to obtain a dispersion having a viscosity at 25 degreesC and at a shear rate of 10 (1/s) of 500 mPa.s. The dispersion (1000 g) was subjected to ultrasonic vibration at 50 degreesC for 30 minutes so as to obtain a dispersion having a viscosity at 25 degreesC and at a shear rate of 10 (1/s) of 1800 mPa.s. This dispersion was coated on a surface-treated polyethylene terephthalate film and dried at 80 degreesC for 5 minutes so as to obtain an ion-exchange film (30 mum thick) having a tensile strength of 10 MPa and a breaking elongation of 16 %.