New ultra-lightweight sludge-red mud ceramics (ULS-RMC) were prepared by red mud (RM),clay and dried sewage sludge (DSS).The properties and mechanism of RM in the preparation of ULS-RMC were discussed.The chemical components,thermal properties and mineral phases of RM were determined by energy dispersive X-ray (EDX),differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA) and X-ray diffraction (XRD),respectively.Constant dosage of DSS to clay and different amounts of RM were utilized in the preparation of ULS-RMC.Physical properties test (bulk density,grain density,water absorption and expansion ratio),XRD and scanning electron microscopy (SEM) were employed to characterize the ULS-RMC.The results show that RM exhibits high hydroscopic property and good water-retention property,and bloating property and fluxing property of RM are caused by abound of gaseous components and flux,respectively.The two chemical properties are utilized to discuss the mineral phases and microstructures differences between ULSC and ULS-RMC.