In this paper, fabrication process of SiO2-BN composite ceramics by aqueous gelcasting method is studied. The rheological properties of SiO2-BN composite powders in aqueous media is correlated with the electrophoreic behavior, pH value, dispersant content and ball-milling time, etc., SiO2-BN slurry with well fluidity and high solids loading is obtained. It is shown that a premixing solution containing 15wt.% monomer can provide sufficient flexural strength for the green body for 50vol.% SiO2-BN slurry. Fracture photographs illustrate that the starting powders in the green body packed closely due to the polymer networks. The phase composition, relative density, mechanical property and microstructure of the final samples are significantly influenced by the addition of BN. The crystallization of amorphous silica was refrained, the relative density, the flexural strength, fracture toughness and Young’s modulus of SiO2-BN composite materials firstly increased and then decreased with the increase of BN content.