 The viscoelastic properties of rubber materials are caused by the combination of the dual response as an elastic solid and a viscous fluid. This behavior yields in time-dependent mechanical properties, including stress relaxation, creep, energy dissipation, hysteresis, and strain rate. Three different carbon-black reinforced natural rubber compounds were experimentally evaluated under stress relaxation and various constitutive models were fitted to evaluate their viscoelastic parameters. It was found that both the elastic and viscous parameters increased in a non-linear relationship with strain and carbon-black content, and the viscous parameters were dependent on the configuration of the model. The Maxwell and Zener models exhibited fitting values of 76.08 percent and 95.1 percent, respectively, while the Weechart model provided the best fit and can be used to estimate the relaxation process of carbon-black reinforced natural rubber applications. This article was authored by Manuel Alberto Guzmán Sanchez. We are article.tv. Links in the description below.