To develop a new process for phosphorus removal the calcium phosphate crystallization method has been investigated. The metastable zone of calcium phosphate precipitates which is defined by concentrations of phosphate and calcium ions and pH was determined by batch experiments. Phosphorus in wastewaters can be constantly reduced to a sufficiently low level at the metastable reaction zone under the presence of seed crystals. The crystallization method proved to be practicable as advanced technology for phosphorus removal from wastewater through column tests and 50m3/day pilot plant tests over 180 days with a sewage secondary effluent.