Abstract: The shear strength characteristics of a typical expansive rock taken out from Xinxiang City, Henan Province were studied by performing suction controlled direct shear tests using the GDS unsaturated direct shear test system. The test results show that the shear strength of the unsaturated clay rock increases with an increase of the matric suction. The contribution ratio of matric suction on the frictional resistance increases with an increase of the net normal stresses. Dilatancy of the clay rock was observed during the shear stage. Owing to the existence of primary fissures and weak surfaces and the cementation effect of the iron and manganese oxides, the rule between the dilatancy of the clay rock and the applied suction was not clearly.