Abstract: Isochronal plots and a three-parameter linear viscoelastic model were used to characterize the stressrelaxation properties of PVA-H prosthetic nucleus and to analyze the influence of swelling ratio and initial PVA content upon the stress-relaxation properties. The results ofisochronal plots showed that PVA-H prosthetic nucleus followed a linear viscoelastic mechanical property. The three-parameter linear viscoelastic model can simulate the viscoelastic property of prosthetic nucleus well with the fitness more than 0.96. It can be seen from the analysis of parameters in the model that the increase of the swelling ratio will greatly increase the speed of dissipated stress of the prosthetic nucleus, and does not have too much influence on the total dissipated stress; but the increase of the initial PVA content will decrease both the speed and the total of the dissipating stress.