Polycrystalline and amorphous mullite fibers are employed as reinforcing phases in preparation of silicabased ceramic cores, respectively, and the effects of mullite fiber types on property of ceramic cores are investigated. Amorphous fibers are not so obvious as polycrystalline fibers in promoting crystallization of cristobalite, reducing shrinkage, and increasing porosity. Compared to polycrystalline fibers, the amorphous fibers have disordering structure similar to silica glass, they are easy to form tight binding with the matrix, enhancing the strength and creep resistance of ceramic cores. Moreover, the metastable structure of amorphous fibers ensures the high chemical activity in alkaline solutions, and the ceramic core exhibits excellent leaching rate. The silica-based ceramic core with a mass fraction of 3% amorphous mullite fibers exhibits excellent comprehensive performance, with bending strength of 27.7 MPa at room temperature and 22.4 MPa at high temperature, high temperature creep deformation of 0.31 mm, and leaching rate of 1.26 g/min, which can well meet the casting requirements of hollow blades.