Abstract: The biological soil crusts BSC play several important roles in many arid and semi-arid ecosystems around the world. Their effects on soil hydrology,however,are poorly understood.The experiments under 15 Bar Ceramic Plate Extractor,Star-1 soil hydrophysical characteristics determination system,and with the van Genuchten closed-form equation for predicting the hydraulic conductivity of unsaturated soils are conducted using two samplers of the BSC and the shifting dune sand.The results indicate that the water holding capacity of BSC is 3 to 9 times magnitude than that of shifting dune sand;when the matrix potential varies from -1 to -3 000 cm,the unsaturated soil hydraulic conductivity of BSC is about 12% lower than that of the dune sand,while the matrix potential varies within -3 000- -15 000 cm,the comparable value for BSC is about 9.10% and higher than that of shifting dune sand.The particular structure and particle size distribution contribute to the variation of the unsaturated soil hydraulic conductivity of the two soils,where biological crusts are formed by living organisms and their by-products,creating a crust of soil particles bound together by organic materials.It improves the micro-habitat of desert soils and increases the availability of soil moisture to shallow rooted shrubs,herbages and micro soil animals in the artificially re-vegetated ecosystems.