Cordierite powder of high purity and cordierite-ZrO2 composite powder were synthesized by colloidal processing. Cordierite was synthesized by calcining a precursor gel obtained by gelation and coprecipitation of AlOOH sol, SiO2 sol and Mg(NO3)(2). The calcination temperature affected the constituent phases in the powders. The phase assemblage in calcined powder affected the sintering conditions. The optimum sintering temperature of the powder with cordierite single phase was 1440-1450 degrees C when it was calcined at 1270 degrees C. The sintered body had a dense microstructure with submicrometre grains. Addition of ZrO2 sol resulted in reaction with cordierite to form mostly ZrSiO4 at the sintering temperature. Several properties of cordierite and cordierite-ZrSiO4 composite, such as thermal expansion coefficient, bending strength, dielectric constant and insulation properties at high temperature, were investigated. Thermal expansion and electric properties were degraded by an increasing amount of ZrO2 additive, whereas the bending strength was improved by the addition of ZrO2.