Abstract: Simulating earthquake loading conditions, a series of cyclic triazial compression tests was carried out on undisturbed samples of cohesive soils from Tianjin so as to investigate the dynamic shear modulus and damping ratio. It has come to the conclusion that the variation of damping ratio, as well as shear modulus, with strain amplitude can be expressed by an empirical formula. The normalized form of shear modulus vs. strain amplitude will be shown by a single curve, and that of damping ratio vs. strain amplitude by a family of curves or a band zone with shrunk ends. The view-point about the law of damping ratio varying with strain amplitude has been developed. A comparison between the measured values from laboratory test and those based on seismic survey for the elastic modulus has been made, and a reasonable agreement has been obtained. For some of cohesive soil strata in Tianjin, some data available for seismic analyses have been provided.