Shell for investment casting is key in obtaining casting with high performances. In this study, carbon fibres were mixed with slurry, silica sol, and sanding materials to prepare fibre reinforced shell for investment casting. Suspension properties, slurry viscosity, and shell strength were all investigated. Failure surface of shell was observed by scanning electron microscopy (SEM). Results indicated that suspension percentage and viscosity of slurry containing fibre and silica sol were higher than those of fibre free slurry. The viscosity of slurry increased as carbon fibre length rose. Comparison of different mixing methods and fibre lengths revealed that addition of carbon fibre with 4 mm in length into silica sol under ultrasonic agitation yielded maximum bending strength of 3.97 MPa. SEM data illustrated that the longer fibres might increase bonding area, leading to increased shell strength.