The stationary acceleration responses of layers were obtained from the vibration tests of saturated sand layers on the electrodynamic type vibration table. By applying the sear vibration theory with uniform rigidity to them, values of sher wave velocity and damping constant were evaluated and the variation of these values with increasing deformation of the sand layer during vibration was examined.
　values of rigidity are found to be strongly dependent on the effective overburden pressure. In addtion, it is found that the vibrational characteristics of saturated sand layers is approximately equivalent to that of dry sand layers in a small deformation range, assuming sand grains to move completely together with water and the rigidity corresponding to the effective overburden pressure to be used.
　While in a large deformation range, the rigidity reduces rapidly due to the effect of pore water.
　Above-mentioned results are also re-examined using the shear vibration theory with linearly-varying rigrdity.