Highly efficient silica products are widely used in the semiconductor industries. Generally this type of silica is produced by a liquid-phase method, which entails various limitations. In this communication, we report a method for manufacturing silica in the gaseous phase by hydrolyzing alkoxysilane. The operation conditions of the gaseous-phase reactions during the synthesis of silica were optimized. The influences of temperature, gas flow rate and concentrations on the reaction kinetics (particle production rate) were also investigated. Products were characterized by SEM. Results indicated that the silica particle diameters could be controlled by changing reaction conditions.