Abstract: Waste aluminum slag and silicon rock were employed as main raw materials to synthesize mullite.Different amount of fine silicon powder mineralizer was added to the prescription,and the crystalline phases and microstructures of the synthesized mullite are investigated by means of XRD and SME.The results showed that the amount of stable mullite was up to the highest(88.1%) with 4.0% mineralizer,and so 4.0% fine silicon powder content is suggested.