Effects of the concentration of ZrOCI,, calcination temperature, heating rate, and the size of secondary particles after hydrolysis on the preparation of high-purity ZrSiO, fine powders from ZrOCI,.SH,O (0.2M to 1.7M) and equimolar colloidal SiO, using sol-gel processing have been studied. Mechanical properties of the sintered ZrSiO, from the highpurity ZrSiO, powders have been also investigated. Singlephase ZrSiO, fine powders were synthesized at 1300°C by forming ZrSiO, precursors having a Zr-0-Si bond, which was found in all the hydrolysis solutions, and by controlling a secondary particle size after hydrolysis. The conversion rate of ZrSiO, precursor gels to ZrSiO, powders from concentrations other than 0.4M ZrOCI,*SH,O increased when the heating rate was high, whereupon the crystallization of unreacted ZrO, and SiO, was depressed and the propagation and increase of ZrSiO, nuclei in the gels were accelerated. The density of the ZrSiO, sintered bodies, manufactured by firing the ZrSiO, compacts at 1600" to 1700°C, was more than 95% of the theoretical density, and the grain size ranged around 2 to 4 km. The mechanical strength was 320 MPa (room temperature to 1400"C), and the thermal shock resistance was superior to that of mullite and alumina, with fairly high stability at higher temperatures.