Calcareous sand is widespread in tropical marine environment regions.It has unique hydro-physical properties which are quite different from terrigenous sand.This study reports a laboratory investigation to the permeability of calcareous sand collected from a coral island in the South China Sea.Through the traditional permeability test,the relationships between flow velocity and hydraulic gradient have been measured for the calcareous sands.To investigate the effect of particle size distribution on the permeability,calcareous sand specimens with varied uniformity coefficients Cu and curvature coefficients Cc have been tested.A significant permeability dependency on the particle size distribution can be recognized from the test results.In light of the unique properties of calcareous sand,shape parameter Ψ(the ratio between sphericity Φ and circularity X)has been introduced to quantitatively describe the particle shape based on the SEM images.In order to explore the effect of particle shape on the permeability of the calcareous sand,an investigation has been performed by comparing with Fujian standard sands and glass spheres with the same particle size distribution and relative compaction.The results indicate that,compared to the other two kinds of granular materials,the particle shape of the calcareous sands is more irregular,which can significantly reduce the permeability of this material.