Matric suction plays an important role in stability of residual soil slopes against rainfall. Changes in matric suction during rainfall are controlled by infiltration characteristics of the soil. Both Soil-Water Characteristic Curve (SWCC) and unsaturated permeability function (kw function) have significant effects on the infiltration characteristics of the soil. The matric suction in the soil can be computed using the governing flow equation with input of SWCC and kw function. The variability in unsaturated soil properties such as SWCC and kw function will result in uncertainties in the computed matric suction in the soil during rainfall. Consequently, uncertainty in matric suction will affect the computed Factor Of Safety (FOS) for slope stability. In this study, confidence limits of SWCC and kw function of residual soils derived from Bukit Timah granite in Singapore are computed using the experimental data from published literatures. The variability in the computed matric suction and FOS as a result of uncertainty in SWCC and kw function is presented by analyzing a typical slope with constant boundary conditions and varying soil properties (i.e. SWCC and kw function). The effects of variability in SWCC and kw function on the infiltration and slope stability are discussed in this paper.