In order to prevent and mitigate disasters due to slope failure, it is important to evaluate the likelihood of slope failure quantitatively by considering the soil properties. It is known that the residual decomposed granite soil on slope has an interparticle skeletal structure. Therefore, in order to examine the deformation and strength characteristics, it is necessary to evaluate the effects of the interparticle skeletal structure by using a completely undisturbed sample in the laboratory. However, it is not easy to procure such a perfect sample due to the difficulty of sampling, for instance. In this study, in order to examine the effect of the interparticle skeletal structure of residual granite soil on the deformation and strength characteristics, consolidation test with bender elements, constant pressure direct box shear test and unconfined compression test were performed using gypsum-mixed decomposed granite soil specimens in which the mechanical characteristics of undisturbed decomposed granite soil specimen were simulated. The test results suggest that the interparticle skeletal structure of residual decomposed granite soil has a considerable influence on the deformation and strength characteristics under the conditions of low confining pressure in which the slope failure often occurs.