Abstract: Fault gouge is an important factor which influences fault movement.In this paper the relationship between mechanical properties of gouge and water content is studied by using the experimental data of gouge from five major faults in China.It is found that viscosity.Young's modulus,compressive strength and residual volumetric strain decrease with water content increasing.There is no clear relationship between bulk modulus,wave velocity shear strength and water content.Natural gouge is a mixtutre of clay,debris and water,in which water takes a more complicate role than does the water in the latter two.The importance of the experiment of this kind,therefore,is visible.