Abstract: A method of producing potassium sulfate consists in conversion of sodium sulfate with potassium chloride in an aqueous medium to yield glaserite and a glaserite solution. Then, the glaserite is decomposed with potassium chloride in water to obtain potassium sulfate and a sulfate solution which is returned to the first stage of conversion. The glaserite solution is cooled at temperatures ranging from +3.degree. to -8.degree. C., whereby mirabilite and a chloride solution are formed, the latter being evaporated to obtain sodium chloride and a concentrated chloride solution. Finally, the concentrated chloride solution is mixed with mirabilite, and the resulting suspension is delivered to the first stage of conversion of sodium sulfate with potassium chloride. The proposed method permits producing high-quality potassium sulfate with full utilization of the return solutions. The yield of potassium sulfate reaches 98.6% at a K.sub.2 O content of up to 53% by weight.