The microstructure and resistivity of AIN/BN ceramic nano-composites and micro-composites were investigated. The results showed that because the nano-BN crystals were homogeneously dispersed around the AIN grains of the matrix, the conductive glass phase surround AIN grains were separated, and it was difficult to form the electric conductible consecutive passageway (than micro composites), the leakage conductance of nano-composites was far lower than micro-composites.