A coated silicon nitride (Si 3 N 4 ) powder with yttria and alumina precursors as sintering additives was prepared by a heterogeneous precipitation method. The rheological and electrophoretic properties of the suspensions obtained from the coated (CO) powder were investigated and compared with those of pure Si 3 N 4 powder and of the mechanically mixed (MM) powders of Al 2 O 3 , Si 3 N 4 , and Y 2 O 3 . The results showed that the CO powder calcined at 500°C exhibited improved dispersion properties compared with the pure Si 3 N 4 powders. The CO powder possessed the surface character of Al 2 O 3 and Y 2 O 3 particles, that made it easier to process in aqueous media, yielding a higher solid loading than the pure Si 3 N 4 powder. These improvements were attributed to a change in the resultant interaction forces between particles from attractive (pure Si 3 N 4 , and MM powders) to repulsive in the case of the CO powder. A homogeneous distribution of sintering additives in the Si 3 N 4 matrix was obtained.