TiN/ZrN multilayers were fabricated using reactive radio-frequency magnetron sputtering methods. X-ray diffraction analysis was used to determine the modulation structure of the multilayers. Using high-resolution transmission electronic microscopy, the interface was found to be a mixed layer of 2—3 nm in thickness. The nano-indentation measurement showed that the hardness of TiN/ZrN multilayers varied with the modulation period. Both the hardness and elastic modulus had their maximums for the multilayer with a modulation period of about 15.24 nm. The enhancement in hardness is discussed with different hardening mechanisms. The interface states and preferred orientation are assumed to be the main causes of the enhancement of TiN/ZrN multilayers in hardness.