The bauxite-based refractory castables are made up of well-graded bauxite aggregate, binding matrix, and a sufficient amount of water. There are four mullite samples with various percentages of sol such as 2%,5%,7% and 10% were added to the alumina castables compositions. The conventional castables processing is carried out and after heat treatment the resultant product is characterized. Prepared castables are characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Differential scanning calorimetry (DSC) to obtain the structural properties, morphology, and thermal analysis, respectively. Enhanced properties were obtained for the mullite samples with 5% and 7% sols. Considerably improved flexural strength, modulus of rupture (MOR) and pH levels are obtained for the mullite gel composition but with a relatively lower level of permanent linear change (PLC). Great refractory properties were achieved after sintering at 1300 ^oC due to the presence of mullite in the bond phase with very slight CaO. This enables their use in various refractory applications such as in steel ladles, furnaces, kilns, incinerators, and reactors

Keywords: Mullite, Alumina, Refractory castable, Characterization, XRD, Microstructure