The high average thermal expansion required for thermal compatibility of dental porcelain with their substrate alloy is supplied by the mineral leucite (KAlSi2O6). In the research, the high thermal expansion coefficients phase leucite was prepared by coprecipitation technique. Three materials with formulae of K2O∶Al2O3∶SiO2 = 1∶1∶x ( x=1.4, 2.0, 4.0 ) were investigated for differences in phase, thermal expansion. Unstoichiometric composition where K2O and Al2O3 were added properly is advantage to leucite obtained. Coprecipitation processing produced fine leucite powder that would sinter at 1300°C, this temperature is about 200°C lower than of melting method. The average thermal expansion coefficients of leucite is 22.7×10-6/°Cfrom room temperature to 620°C,which is higher than the common porcelain. Changing in the leucite content of dental porcelain would results from thermal expansion coefficients of porcelain variation, which could be responsible for changes in porcelain-metal thermal compatibility.