Silica ceramic cores have played an important role in the manufacture of hollow blades due to its excellent chemical stability and moderate high-temperature mechanical properties. In this study, silica-based ceramics were prepared by stereolithography and the influence of Al2O3 content on mechanical properties of the silica-based ceramics was investigated. With the increase of Al2O3 content, the linear shrinkage of the silica-based ceramics first decreased and then increased, while the room-temperature flexural strength and the high-temperature flexural strength first increased and then decreased. As the Al2O3 content increased to 1.0 vol.%, the linear shrinkage was reduced to 1.64% because of the blocked viscous flow. Meanwhile, the room-temperature flexural strength and the high-temperature flexural strength were respectively improved to 20.38 MPa and 21.43 MPa with 1.0 vol.% Al2O3 due to the increased α-cristobalite and β-cristobalite content. Therefore, using the optimal content of Al2O3 in silica-based ceramics can provide excellent mechanical properties and ensure the reliability of silica-based ceramic cores for manufacturing hollow blades.