This paper describes the anisotropy of Knoop hardness in olybdenum single crystals neutron-irradiated at high temperatures in the Fast Experimental Reactor (JOYO) and the Fast Flux Test Facility (FFTF/MOTA). Knoop hardness, measured on the (001) surface of the specimen, showed a maximum in the [100] indentation direction and a minimum in the [110] direction. This anisotropic behavior in body-centered-cubic metals remained the same after neutron irradiation, though the average hardness increased. The degree of relative anisotropy, i.e. the hardness ratio between [100] and [110] directions, however, decreased with increasing neutron fluence. The hardness anisotropy was analyzed using the average Taylor factor.