Abstract: Using H₃PO₄,HAc and HCl as gelating agents,in a wide range of pH,temperature effect on the rate of gelation of silicic acid was studied at 0°,20°,30°,40°,50°,and 70°.Activation energy of gelation was obtained therefrom.The results indicated that the activation energy varied with the kind of gelating agents used and pHof the solution.It was found also that concentration of silicic acid had an effect on the activation energy of gelation,however,when the total salt concentration of the solution maintained constant,the activation energy would not change with the concentration of the acid.All these findings had been well explained by the theory of polymerization of silicic acid proposed previously.