Within the framework of strain space plasticity approach for cyclic mobility (Iai et al, 1990), this paper shows how to represent the realistic hysteretic damping factor under cyclic loading. In the present approach, actual cyclic shear mechanism is decomposed into a set of one dimensional virtual simple shear mechanisms.
　Four parameters defining the virtual simple shear mechanism under cyclic loading condition are identified with the soil parameters measured by the cyclic simple shear test.
　The paper also show how to identify the rest of five parameters defining the cumulative volumetric strain of plastic nature for representing cyclic mobility. The undrained cyclic test results, which are commonly available in the practice of soil dynamics and earthquake engineering, are fully utilized for the parameter identification.