Abstract：In order to study viscoplastic properties of clay，uniaxial compression tests are performed with computer-controlled triaxial apparatus on saturated，wet，air-dried，and oven-dried Japanese Pleistocene clay (Fujinomori clay：specific gravity Gs = 2.69，D50 = 0.017 mm，coefficient of uniformity Cu = 10，plastic limit IP = 33%，liquid limit IL = 62%). In the tests，axial (vertical) strain rate was changed stepwise for many times，and drained creep tests were performed for several times during monotonic loading at constant strain rate. Global unloading and reloading were also applied. Results of the tests on the Japanese Pleistocene clay with different water contents(different saturations) were presented. The results show that viscous properties of the Japanese Pleistocene clay with different water contents are significant in all the tests. Load rate effect (i.e.，the stress changes immediately after change in the strain rate occurred in the stress-strain curve) and creep deformation can be seen clearly in all the tests. The analytical test results show that：(1) viscous behaviour of Japanese Pleistocene clay does not appear due to the delayed dissipation of excess pore water pressure(not only saturated and wet but also air-dried and oven-dried specimens show significant viscous behaviour)；(2) viscous properties of specimens with different saturations are similar (load rate effect and creep deformation were observed in all the specimens with different saturations)；and (3) the stiffness of specimen with different saturations increases significantly after creep. In addition，a nonlinear three-component model is proposed，which can simulate well the viscous properties of clay.
