Sewage sludge gasification can result in significant environmental benefits. However, the influence of sewage sludge on the process is not recognized in an adequate degree. The purpose of the present study was to investigate the ash fusion temperature (AFT) of coal-sewage sludge (SS) and the influence of phosphorus on it. Ash fusion characteristics of six types of coals, one type of sewage sludge, and the corresponding coal-sewage sludge blends were measured. Chemical and mineralogical compositions of blended ashes at different temperatures were determined. Ash fusion temperatures of most coals are lowered by adding sewage sludge, because Ca and Na in sewage sludge ash can react with refractory minerals from coal to form low temperature eutectic. The influence of phosphorus on mixture AFT depends greatly on the Al2O3/(CaO + Na2O + K2O) (A/CNK) molar ratio of bulk ash. Phosphorus tends to react with calcium to form refractory minerals in subaluminous systems (A/CNK<1), but mainly exists in amorphous materials and beneficial for decreasing ash fusion temperature in peraluminous systems (A/CNK>1). (C) 2013 Elsevier B.V. All rights reserved.