Due to the nonlinear viscoelasticity observed in moisture solids or polymer materials, it is generally difficult to analyze their deformation problems because the analysis requires complex constitutive equations. A typical analysis technique that employs a generalized viscoelastic model involves considerable amount of effort in the evaluation of material parameters, and it is difficult to apply the analysis technique to finite element simulation. On the other hand, fundamental constitutive models such as those proposed by R. Hooke, C. Maxwell and W. Voigt are useful in the simulation of various industrial problems. In this study, the technique for the evaluation of the nonlinear parameters in the three-element solid model, one of the fundamental models, is presented and used to analyze viscoelastic problems. The technique uses the simple tensile tests for 3 different strain rates. In one case, the strain rate is very slow and viscosity can be neglected and, while in the other two cases viscocity is not negligible and is evaluated from the strain rates. By the sequential application of the technique from a low stress level to a higher level, the nonlinear parameters of the three-element solid model, which can be defined to depend on state quantities, can be evaluated. The reliability of the technique is also examined by studying its application to the evaluation of the mechanical behavior of biological soft tissues, which are of moisture solids. In addition to the fundamental procedure of the evaluation presented in former section, the modified procedure is also shown to evaluate more precise parameters by improving the experimental condition.