The presence of cracks can trigger landslide after rainfall. The saturated/unsaturated hydraulic conductivity is a key parameter to study the slope stability. In this research a random crack is made using high-resolution machine. An apparatus is developed to conduct seepage experiment through the random crack; and the saturated hydraulic conductivity of the crack can be obtained. The unsaturated hydraulic conductivity is predicted using the saturated hydraulic conductivity and the soil water characteristic curve. Results show that the saturated hydraulic conductivity is 0.1 m/s when the average aperture of the random crack is 0.4 mm. The hydraulic effective aperture is 0.35 mm

which is smaller than the average aperture. The hydraulic conductivity is proportional to the square of the average aperture

which is consistent with the cubic law. The unsaturated hydraulic conductivity curve shows that the hydraulic conductivity decreases very fast when the matric suction is larger than the air entry value. When the matric suction reaches the suction corresponding to the residual water content the influence of matric suction on the hydraulic conductivity is limited. Finally

the hydraulic conductivity approaches a constant value.