Calcium and magnesium were widely distributed over the world and the use have been increased gradually. Under these circumstances, the reaction of dolomite with NH₄Cl was carried out to develop a new process for the extraction of calcium and magnesium and to find the fundamental data for the reaction mechanisms from the reaction products. The overall reaction mechanism was as follows : CaMg（CO₃）₂+4NH₄-Cl→MgCl₂+CaCl₂+4NH₃+2H₂O+2CO₂. And the optimum condition for the reaction of dolomite with NH₄Cl was as follows; reaction temp. : 450℃, reaction time : 30 min, weight ration(NH₄Cl/Dolomite) : 8.0, N₂ gas flow rate : 30cm³/min, particle size(av.) : 69 m. Under the above condition, dissolved magnesium and calcium was 85.48%, 99.63% reapectively.