The behavior of thermoplastics depends on several factors, mainly time and temperature. The present work is the a study of the dependence of these materials on time. The material considered in this study is a polyamide 6. The applied behavior model is represented by the Kelvin-Voigt viscoelastic mechanism. the mathematical formulation of the equations of the model is put in place and tensile tests at different strain rates are conducted. The parameters model are then identified. These being sensitive to the strain-rate, the relation which links them with it is established by means of an exponential regression. The results test-model are presented and dicussed.