Si(3)N(4)-B(4)C composites containing fine and coarse B(4)C particles were produced using Al(2)O(3) and Y(2)O(3) as sintering additives via spark plasma sintering (SPS) technique. Phase assemblages of the produced composites were determined by XRD analysis. Si(3)N(4), B(4)C and in situ formed SiC, h-BN and Si phases were observed. Even when incorporated in significant amounts, B(4)C was consumed readily in the Si(3)N(4) based system. Consequently, full densification of these composites was found to be a very difficult task due to the simultaneous in-situ reactions, even in fast sintering process. Electrical resistivity measurements carried out at room temperature indicated that addition of both fine and coarse B(4)C particles decreased the electrical resistivity by several orders of magnitude due to the formation of electrically conductive in-situ phases, mainly SiC and metallic Si.