This study have been carried out to investigate the conditions which calcium sulfoaluminate(3CaO.3Al(2)O(3).CaSO4) is formed when the mixtures of alunite and limestone are sintered. Alunite reacts with limestone at 800similar to1300 degreesC as follows. K2SO4.Al-2(SO4)3.4Al(OH)(3) + 6CaCO(3) --> 3CaO.3Al(2)O(3).CaSO4 + 2CaSO(4).K2SO4 + 6H(2)O(g) + 6CO(2)(g). Then calcium langbeinite (2CaSO(4).K2SO4) is formed at 700 degreesC and calcium sulfoaluminate, at 800 degreesC and those are stable to 1300 degreesC. But when SiO2 is contained in alunite or limstone, to firm the formation of calcium sulfoaluminate the molar ratios of CaO/alunite and CaO/SiO2 must be kept over 6.0 and over 2.0, respectively. A clinker composed of calcium sulfoaluminate and calcium langbeinite reacts with ordinary portland cement(OPC) to form ettringite(3CaO.Al2O3.3CaSO(4).32H(2)O) in water as follows; 3CaO.3Al(2)O(3).CaSO4+2CaSO(4).K2SO4+7Ca(OH)(2)+5CaSO(4).2H(2)O+80H(2)O-->(3CaO.Al2O3.3CaSO(4).32H(2)O)+2KOH, as calcium langbeinite is transformed into CaSO4.2H(2)O and K2SO4 and K2SO4 reacts with the Ca(OH)(2), the hydrates of OPC, to form CaSO4.2H(2)O in water. When we replace 10% of OPC, the mixed cement shows high early and lately strength.