Abstract: The slaking property is studied experimentally and theoretically on the basis of the slaking process observation and slaking mechanism research of six types of swelling rocks. The slaking is different from the swelling and fissuring of expansive rock. The effects of slaking on cut slope stability especially on topsoil slip of swelling rock are mainly reflected by the decrease of shearing strength parameters c and φ with the increase of hygroscopic moisture content. It is reasonable that topsoil slip of swelling rock cut slope is mainly caused by its slaking because the calculated depth of topsoil slip mass is the same as the thickness of strong slaking layer determined by cone penetration test.