Effects of SiO₃^2- in natural source water on phosphate removal by FeSO₄/KMnO₄ process are investigated. The removal efficiency of phosphate increases firstly and decreases subsequently with the increase of pH values in the presence of SiO₃^2-. The present of SiO₃^2-(1.0 mmol/L) promotes the efficiency of phosphate removal in pH values of 4―6 and removal of phosphate enhances by 6.0%, 9.9% and 6.3%. In contrast, with the increase of pH values (7―9), removal of phosphate significantly decreases by 14.76%，32.6% and 17.3%. SiO₃^2- reduces the surface ζ potential of floc particles formed in situ and increases the amount of residual iron in the solution. In addition, SiO₃^2- has a certain influence on composed elements and surface features for floc particles formed the KMnO₄/FeSO₄ process. The results provide a necessary theoretical foundation for the practical application of KMnO₄/FeSO₄ process for phosphate removal.