In the present study, water-retention behaviour of sand during drying and wetting process has been observed microscopically using micro x-ray computed tomography (CT). CT images taken at different water-retention states during drying and wetting paths are trinarised to segment the images into the soil, water and air phases. The segmentation technique using region growing method takes into account uniform distribution of the mixels to reduce the inherent partial volume effect. Using the trinarised images, local porosity and degree of saturation are calculated for the cubic subsets centered at reference points, and then frequency maps of the two local values are drawn. Through the comparison of the frequency maps, the relation between the local porosity and the degree of saturation and the changes in the relation during drying and wetting process are discussed.