Abstract: Investigates the influence of such cosolvents as n-butanal, isopropanol and ethanol on the reaction time and yield in the precipitation process and sol-gel process of tetraethyl-orthosilicate hydrolysis. The structure and morphology of powdered SiO2 were studied by TEM and FT-IR. The results showed that the reaction time decreases and yield increases with the increase in alkyl chains during either precipitation process or sol-gel process. In addition, the structure of powdered SiO2 obtained from either process are the same, but the particle sizes of SiO2 powder obtained from different hydrolysis process in which different cosolvents are used are different, ie. Using the cosolvents n-butanol and isopropyl can form smaller particle size than using ethanol.