PURPOSE: To solidify KOH at a low temperature with saved energy in a relatively simple process, by heat-treating a complex in which a high-boiling alcohol incorporates KOH and water under reduced pressure, removing the water and further removing the alcohol with an organic solvent.

CONSTITUTION: An alcohol having ≥160°C boiling point, e.g. n-decanol, n- dodecanol, etc., is brought into contact with an aqueous solution of KOH in a high concentration, preferably 45W60wt% to form an alcoholic caustic potash incorporation complex in which the KOH and water are incorporated. The complex is then heat-treated under reduced pressure (normally heated at about 50W150°C under 1W50mmHg reduced pressure for several minutes W several hours) and the alcohol is extracted with an organic solvent, e.g. acetone, etc., to obtain the aimed solid KOH. The KOH can be solidified with saved energy and without requiring the use of a high-class material for an apparatus in a low temperature process as compared with a conventional boiling down process.