The properties of aqueous colloidal silica sol synthesized by an ion-exchange in a waterglass solution were examined and a continuous manufacturing process of silica sol and regeneration was designed for producing silica sol from inexpensive starting materials in large quantities. The maximum ion-exchange capacity of resin, the ion-exchange kinetics, and the characteristics of the silica sol were evaluated. The process conditions for the continuous manufacturing process of silica sol were optimized. Silica sols synthesized by the continuous manufacturing process have silica contents in the range of 5-5.7 wt %, a pH of the sol in the range of 2.3-3.0, and a low residual sodium ion concentration. In terms of possessing a narrow deviation from the mean value of these properties, this process can manufacture reliable silica sols on a mass production level.