Fused silica ceramics prepared by gel casting method. We studied the effect of temperature and time on the crystallization and microstructure of this ceramics at 1200, 1250, 1275, 1300 and 1350℃ for 1,2,3,4 and 5 hours.Results shows that to avoid the formation of crystalline phase in the bodies, these parts should be sintered at temperatures less than 1300 ° C. The best conditions for sintering this bodies is temperature at 1250 ° C for 5 hours, the density, porosity and water absorption of pieces that were obtained in this condition respectively were 1.95g/cm3, 10.47% and 5.83% .