Confined compression stress relaxation tests with porous platens (Fig 1) have been frequently used for investigating the flow-dependent viscoelastic behavior of biological hydrated soft tissues [Lai et al., 1981; Mow et al., 1980]. From experimental data, the one-dimensional (1D) compression modulus (i.e., the aggregate modulus) at equilibrium and the hydraulic permeability of the tissue can be calculated using the biphasic theory for cartilage developed by Mow et al. (1980). However, the swelling pressure effects associated with fixed charge density (FCD) can not be accounted for directly by the biphasic theory. Thus, in this abstract, we determine the effects of FCD, hence the osmotic pressure, on the confined compression stress-relaxation behavior of cartilage using our mechano-electrochemical theory [Lai et al., 1991]. The objectives of this study are to determine the confined compression stress-relaxation behavior of a charged, hydrated-soft tissue by: 1) delineating the contribution of the swelling pressure to the total stress when the tissue is compressed; 2) determining the deformation, flow, pressure and electric fields in the tissue for the understanding of mechano-electrochemical signal transduction within the tissue.