Although hysteretic phenomena which appear during the infiltration of water or nonaqueous phase liquids (NAPLs) into soil play an important role on various field problems, only few fundamental studies have been done so far on the expression of soil water characteristics and unsaturated hydraulic conductivity with hysteresis. In this paper a new method is proposed to express the phenomena associated with soil water characteristics in a mathematical way which imposes two conditions obtained from experimental results. And the theoretical results compared quite favorably with experimental results. This method enables one to evaluate hystretic relationships of θ (h) by providing the parameters for main dry curve and main wet curve together with some informations on scanning curves. A new method for evaluating hysteretic relationships of unsaturated hydraulic conductivity is also proposed and the calculated results agreed well with all the conditions based on qualitative characteristics obtained from various experimental data.