Abstract: This article briefly summarizes the synthesis and characterization of ultrafine SiO 2 .Using Na2 SiO3 · 9H2 O as source of silica ultrafine SiO 2 were obtained by precipitatin process .In this work some influences of sodium silicate concentration , calcining heat and ultrasonic treatment on the synthesis of ultrafine SiO 2 were discussed .The results show that the optimal preparation condition Is , sodium silicate concentration is 0.20 g/mL, and calcination condition is 600 ℃, 4 h.N2 adsorption-desorption isotherms, XRD, FT-IR and some other experiment methods were used to investigate the structure and other physical properties of the samples .The results show that the SiO 2 are amorphous , and the BET specific surface areas of the samples are larger than 400 m2/g.

Key words: ultrafine SiO2;precipitation method;Na2 SiO3 · 9H2 O;ultrasonic