Abstract: Ultrafine nodular silica powder was prepared by the controlled hydrolysis of sodium silicate in chlorination ammonia solution at befitting temperature and pH value. The relationships between the time required for powder formation and reacting temperature, pH value, concentration of sodium silicate solution and its flowrate were discussed with some parameters determined for the preparation, i.e., pH value 9, reacting temperature 60°C and concentration of sodium silicate 0.6 mol·L^-1. In addition, the relevant sintering behavior at different temperatures for SiO2 was investigated. The results revealed that the ultrafine silica powder would be sintered when the temperature is over 900°C. The structure of nodular powder particles was characterized by TEM and SEM, and the results showed that the silica powder was really of nodular nano-meter particles.