TiC/Mo multilayers with modulation wavelength ranging from 2.5 to 13.7 nm were prepared by ion beam assisted deposition (IBAD) system at nearly ambient temperature. The individual layer thickness was maintained to be equal. Mechanical properties of these multilayers were thoroughly studied. The structures were analyzed by X-ray diffraction. The hardness and elastic moduli of these multilayers were determined using a nanoindentation facility. The nanohardness showed a strong dependence on the modulation wavelength. It was found that the multilayer hardness was greater than the volume weighted mean of the component hardness. With the modulation wavelength adjusted, the multilayer was even harder than its hard component (TiC). A maximum hardness of 21.40 GPa, about one time larger than that of the rule-of-mixture values, was found at lambda = 2.5 nm. Possible mechanism for hardening is discussed.