Cyclic torsional shear and cyclic triaxial tests are performed on undisturbed marine silty clay by the hollow cylinder apparatus; and the shear modulus and Young’s modulus are obtained respectively. Meanwhile

the effect of effective confining pressure and stress ratio on dynamic Poisson’s ratio is investigated on the basis. It is found that the dynamic Poisson’s ratio increases with generalized shear strain

but decreases with increasing effective confining pressure and stress ratio. The effects of effective confining pressure and stress ratio on dynamic Poisson’s ratio is weakened as the generalized shear strain increasing. The dynamic Poisson’s ratio is about 0.48 when the Poisson’s ratio increased to 1.8×10-2 or so

and the tests are terminated. There are no shear dilatation during all tests because the Poisson’s ratios are smaller than 0.5. It is indicated that the undisturbed marine silty clay tested in the paper has a good stability under cyclic loadings