Abstract: Accurate characterization of the anisotropy in unsaturated permeability for soils is significant in simulating flow and contaminant transport. Based on the Mualem’s unsaturated permeability function, the power type expression for the relationship between the anisotropy coefficient and the effective degree of saturation is derived by introducing the pore connectivity-tortuosity parameter so as to describe the nine types of the anisotropy in unsaturated permeability. In the process of anisotropy coefficients varying with the effective degree of saturation, there exists a critical point at which the dominance of flow direction switches. This expression is then validated using the numerical test results of unsaturated permeability of a pore network for modeling the soil samples in the previous literatures. Combining with the Van Genuchten-Mualem function, this expression can be finally used to represent the effect of matric suction on the anisotropy in permeability for four soils in the existing literatures.