A method for producing a porous potassium carbonate, which comprises calcining potassium hydrogen carbonate crystals having a mean particle diameter of from 100 to 1,000 .mu.m at a temperature of the object to be calcined of from 100 to 500.degree. C., while introducing a dry gas which has a dew point of not higher than 0.degree. C. and a temperature of from 10 to 50.degree. C.