Three silicon nitride ceramic balls were prepared via hot static pressing (HIP). In addition to some conventional sintering aids like Al2O3 and Y2O3, TiN, Fe3Si and WC transition metal compounds were incorporated into the powder mixtures before ball-milling and HIP, respectively. The microstructures and mechanical properties of the silicon nitride ceramic balls prepared were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nano indentation (NI) analysis. The results indicate that TiN additive has an effect of suppressing the formation of Si2N2O during sintering. TiN and WC additives can promote the diffusion of Al and O into silicon nitride matrix during sintering, resulting in the formation of some sialon phase. However, Fe3Si additive has little effect as mentioned above. TiN additive has an effect of refining the microstructure, thus obtaining a refined grain structure with an even size distribution. Fe3Si additive tends to produce a microstructure of long-coarse-grain intersected and bridged frame filled by grains. WC additive leads to the development of an uneven microstructure containing the coarser and finer grains. Compared to the balls containing Fe3Si or WC additives, the ball containing TiN additive has better mechanical properties, i.e., higher hardness and greater modulus of elasticity.