The idea of controlled release of high valence counter ions was used in direct coagulation casting of ceramics. Calcium phosphate was used as the high valence counter ions source. Influence of the content of calcium phosphate on the viscosity of the suspension with positive charge on particles and the properties of green body were investigated. The results show that the content of calcium phosphate which leads to coagulation of suspension is 0.150.2 wt%. The pH changes from acidic regime to basic regime after calcium phosphate addition. Hydrochloric acid is consumed and CaHPO4, Ca(H2PO4)(2), and CaCl2 are generated. The electrical double layer of alumina particles is strongly compressed by Ca2+ ions, leading to rapid increase of viscosity. Also, the pH value at high temperature approaches to isoelectric point of alumina and contributes to the instability of suspension. The optimum coagulated temperature is 60 degrees C with coagulation time of 135 min. The compressive strength of green body is up to 2.8 MPa.