Abstract: During reduction of waste activated sludge (WAS) by sludge disintegration, many organic, nitrogen and phosphorus constituents of WAS would be dissolved and released into sludge supernatant. Effective recovering of phosphorus will benefit to stable performance of municipal biological treatment, reuse of WAS and alleviation phosphorus resources shortage. In this paper, phosphorus recovery from sonicated WAS supernatant by magnesium ammonium phosphate (MAP) sedimentation process was carried out and studied. Through the single factor experiment, the optimal reaction conditions was determined finally, which was: pH was 970, reaction time was 10 min, n(Mg2+)/n(PO3-4P) was 15 Under the optimal conditions, the recovery rates of TP and PO3-4P by MAP reached 832%、963%, respectively, meanwhile, partial organics and nitrogen also were removed.