Abstract: The wave and wind loadings applyed on structure foundations with a large number of cycles affect the long-term undrained mechanical behavior of clay, which is one of key issues for the foundation design. Qwing to lack of cyclic tests with a large number of cycles up to now, laboratory tests on over consolidated clay are perfomed to study the cyclic behavior with a large number of cycles (e.g., more than one million). Based on the results of reconstituted specimens with OCR=4, the possible existence of the threshold stress ratio under the symmetric cyclic loading is confirmed. The value of the threshold stress ratio is 0.44~0.48. At the early stage of cyclic loading, the evolutions of axial strain and pore pressure are similar to the results of the conventional cyclic tests. However, as the number of cycles increases, the cyclic axial strain decreases, whereas the permanent axial strain increases and the pore pressure decreases from a positive to negative value. These new phenomena are analyzed by conducting additional creep tests on the overconsolidated clay, which throws new light on studying the mechanism governing the long-term undrained mechanical behavior of overconsolidated clay under cyclic loading with a large number of cycles.