Abstract: Nano-sized silica powder was prepared by in-situ modification method and then organic silica sol was obtained through ultrasonic deagglomeration method，with it as raw material.The influences of type of organic solvent，concentration of silica，and ultrasonic time on the stability of the target system of organic sol were discussed.The relationship between ultrasonic time and viscosity of the sol system was studied.Aggregation and granularity in the sol were characterized under different times of ultrasonic.Mechanism of ultrasonic to deagglomeration of silica powder in organic solvent was explained.It was showed that ethylene glycol monomethyl ether was the best organic dispersion medium，the optimum mass fraction of disper- sion was 4%，the silica powder was with 50~100 nm in aggregate in the organic solvent and the viscosity of silica sol got smaller with the expansion of ultrasonic time.

Key words: ultrasonic, agglomeration, deagglomeration, silica