Mullite is one of the most extensively studied materials in both traditional and advanced ceramics. It is the main constituent in conventional ceramics, such as pottery, porcelains, sanitary wares, refractories, and structural clay products, like tiles and building bricks. Mullite has excellent mechanical properties, high thermal stability, and good corrosion resistance, making it suitable for membrane support applications. Porous mullite ceramics can be made by sintering Al2O3 and SiO2 precursors at high temperatures with or without using pore-forming agents. The use of mineral-based aluminosilicate raw materials as a source of Al2O3 and SiO2 is a promising approach for cost-effective membrane manufacturing. Among them, kaolin or China clay is one of the important raw materials extensively studied to make low-cost mullite membranes or supports. After sintering at high temperatures, the mineral kaolinite in clay undergoes phase transformation to form mullite as the principal constituent. However, a considerable amount of SiO2 glassy phases and cristobalite will also develop during this transformation, deteriorating the support characteristics. The addition of Al2O3 powder along with kaolin is an effective approach to reduce the excess glassy phase and increase the amount of mullite in the matrix. During sintering, secondary mullite crystals are formed by the dissolution and reprecipitation of Al2O3 particles in the glassy phase of the matrix. The excess Al2O3 will stay inside the matrix to form mullite-Al2O3 composite membrane supports. To further enhance the porosity and strength of the matrix, sintering additives, such as metal oxides (MgO, V2O3, MoO3, etc.) and fluoride precursors (aluminum and ammonium fluorides) can be added along with Al2O3. These materials have a significant role in the mullite grain morphology and densification process. The addition of fluoride precursors helps to form needle-shaped interlocking mullite crystals or whiskers in the matrix by a vapor phase reaction. The porous mullite with needle-shaped mullite crystals has excellent pore characteristics and strength, enabling it to use for microfiltration applications directly without the need for an additional membrane layer.