The removal of phosphate from municipal sewage by high gradient magnetic separation using aluminium sulphate as precipitating agent and Fe₃O₄as seeding material was studied. The effects of aluminium sulphate, Fe₃O₄, magnetic field intensity, pH value and flow-rate of sewage on phosphorus removal rate were investigated. The results show that addition of 200 mg/L Al₂(SO₄)₃· 18H₂O and 300 mg/L Fe₃O₄, magnetic field intensity of 200 kA/m, pH value of 4.5 – 7.0 and flow-rate of 6.15 cm/s are both efficient and economic technical parameters for removal of phosphate. The pH value has a tremendous effect on the removal of phosphate. In the pH range of 4.5–7.0, more than 95% phosphate can be removed. Theoretical analysis indicates that the solubility of AIPO₄is minimum at pH 4.0 – 7.0 and the electrostatic attractive force between AIPO₄and Fe₃O₄is maximum at pH 4.5 – 6.5.