Surface-parallel slabbing is a failure mode often observed in highly-stressed hard rocks in underground excavation.To understand the occurrence mechanism of slabbing failure, uniaxial compressive tests and true triaxial compressive tests (with one-direction unloading stress) are carried out for different rocks and rock-like materials.It finds that the occurrence conditions of slabbing failure are not only related to rock type, but also related to specimens height-to-width ratios, stress paths, the medium and the minimum principle stresses.The slabbing strength of hard rock is lower than the corresponding uniaxial compressive strength, which is about equal to 40-60% UCS.Slabbing fractures are usually parallel to the maximum principal stress and almost in equal space.The propagation of slabbing fractures is earlier than that of shear fractures in rocks.