The paper describes the results of an experimental research aimed at studying the effects of relative humidity cycling on the degradation phenomena of two clayey rocks from North-East Spain, with particular emphasis on peak shear strength, low-strain stiffness and water permeability. Undisturbed samples were subjected to an extreme relative humidity cycle (between 15% and 99%) using the vapour transfer technique, before performing triaxial compression and water permeability tests. Rock stiffness was evaluated by ultrasonic pulse tests. Test results showed clear differences in stiffness and shear strength response between undisturbed and degraded samples, highlighting the relevance of hydraulically induced degradation phenomena on this type of materials.