In this work, a novel method for the preparation of colloids has been studied for the fabrication of silicon nitride –Boron nitride composites. In the present work, the dispersion of mixed silicon nitride –Boron nitride powders in aqueous media was studied with the changes dispersant concentration, solution pH etc. Polyethylenimine (PEI) additive as a dispersant were used for Si3N4 and BN powders in aqueous media. Well-dispersed Si3N4 and BN powders in aqueous media were attained atthe 1 wt% PEI and pH 9. 40 vol% covered Si3N4/BN slurries with varying BN content was adapted for gel casting. The gel casted material waspreheated at normal room temperature, debindered at 6000C and sintered at 17000C. The sintered composite material composed mainly of alpha-Si3N4, beta-Si3N4, and h-BN. The prepared composite material shows uniform microstructure with faceted particles, α-Si3N4 and abundant pores.