In this study, anisotropic permeability of a single rock joint with rough surfaces and its change due to shear displacement are investigated using the latest analytical approximation for permeability. The permeability approximation is a function of the spatial correlation of the aperture as well as the statistical parameters (mean and standard deviation) of the aperture distribution. The present approach could well explain the significant increase of permeability due to shear displacement and its gradual approach to an asymptotic upper bound of the permeability. The asymptotic permeability with increasing shear displacement is dependent on the standard deviation of surface roughness. The anisotropy in the permeability was also induced by the shear displacement. Far from the expectation, the degree of anisotropy in rough rock joints with random surface model was more or less negligible, compared with the remarkable increase due to the shear dilation. It was also noticable that the shear-induced anisotropic permeability became more isotropic as the shear displacement exceeded the characteristic correlation length of surface asperities. All these results were compared and verified by the numerical shear flow experiments using the randomly generated rock surfaces. However, it should be noted that the understanding in the study was based on initially isotropic surfaces, and under absence of normal load.