Abstract: The experimental work on Inada granite and Yamaguchi marble was done by using the general triaxial test machine. It is shown that from a certain stress state, while both the maximum and the minimum principal stress were kept constant, the rock rupture can be caused by change of the intermediate principal stress. In this case as a precursor of rupture, the increasing of the acoustic emission appeared much later than that caused by change of the maximum principal stress. The possibility of earthquakes caused by changes of the intermediate principal stress was discussed.