Abstract: Studies of volumetric deformations of shear bands are important to obtain a full understanding of the deformation and failure mechanisms. To study distributions of volumetric strains in shear bands, some monitored lines are arranged at clay specimens in uniaxial compression according to positions of higher local volumetric strains in shear bands when microcracks just occur. Smooth local volumetric strains at these lines are obtained through interpolation from strains based on a digital image correlation method. The evolution of the mean and standard deviation of local volumetric strains along these lines are obtained. The concept of the local dilational angle is proposed. The following results are obtained. Generally, with an increase of the longitudinal strain, the contractive deformation is converted into the dilational deformation in shear bands, while in this process several reciprocal cases may occur. Although specimens in compression continuously undergo contraction in total, local volumetric dilatancy occurs earlier at the longitudinal strain of 0.04~0.09. If the condition for local volumetric dilatancy is regarded as the occurrence of the positive mean of the local volumetric strain at monitored lines, then the local volumetric dilatancy occurs at the longitudinal strain of 0.06~0.14. The migration velocity of the peak local volumetric strain can reach (3.77~8.48)×10^-5 m·s^-1. If monitored lines are determined according to positions of higher local volumetric strains, then the maximum local dilational angle rapidly increases from 13.47°to 56.26° after the mean of the local volumetric strain at monitored lines is changed from negative to positive values, although specimens undergo entire contraction. If monitored lines are determined according to positions of longer shear bands, then the averaged local dilational angle rapidly increases from 16.60°to 45.79°. For specimens undergoing contraction in total, local volumetric dilatancy occurring in shear bands cannot be explained using the traditional dilational angle.