PURPOSE: To obtain the title fine powder useful for a bakable electrocoated film, by dissolving a specified resin in morpholine under applied heat and pressure in a heating/pressurization mixer, subjecting the solution to slow cooling, gradual release of pressure and solvent recovery and drying the obtained powder under agitation.

CONSTITUTION: A polyether sulfonic acid resin is dissolved in morpholine under applied pressure and heat in a nonoxidizing atmosphere in a heating/ pressurization mixer; this solution is cooled slowly to 60°C or below; the pressure is gradually released; and morpholine is recovered under a decreased pressure to obtain a powder. This powder is dried under agitation to obtain the title fine powder of a particle diameter of 40μm or below.