A new synthetic method of producing alpha-MnO2 was investigated. Calcination of a mixture of either manganese carbonate and potassium formate and/or manganese carbonate and potassium butoxide yielded alpha-MnO2 with potassium selective adsorption properties. The temperatures and other conditions to synthesize the materials were determined in advance by DTA-TG and XRD analyses. The product which was synthesized from manganese carbonate and potassium butoxide showed better crystallinity of alpha-MnO2 and higher adsorption selectivity for potassium ion than that from manganese carbonate and potassium formate. It will be an applicable adsorbent in potassium separation for industrial usage.