A series of triaxial compression test was carried out using Holocene as well as Pleistocene clay samples from the seabed of Osaka Bay retrieved as deep as 155m in depth. In the undrained tests, the specimen's deformation was measured locally by using a newly developed system. In each test, the variation of elastic shear wave velocity with stress was also monitored using a set of bender elements. In this paper, not only the compressibility but also the shear characteristics was carefully examined over a wide strain range. In comparing the behaviour between the natural clays and the reconstituted clays, the aging effects were manifested in terms of the deformation-strength characteristics of the natural sedimentary clays.