While the Superpave binder?specification system successfully introduced laboratory?measured performance parameters, the constitutive stress?strain relationship of asphalt binders should be described. The availability of a computationally efficient constitutive relationship would allow to improve the accuracy of predicting the response of asphalt binder to loading and to characterize its viscoelastic properties as well as its relationship to mix performance. To this end, the objective of this study was to provide a theoretical insight into the mechanical behavior of unmodified asphalt binder at low temperatures and to present a constitutive model that may be used to predict asphalt binder's response to loading. To achieve this objective, nine unmodified binders obtained from two asphalt suppliers were tested using the direct tensile test (DTT). A viscoelastic model was formulated and fitted to laboratory measurements obtained at different loading rates. Fitting parameters were then incorporated into a 2D FE model representation of the DTT sample and comparison was established between measured and calculated stress responses. This comparison indicated that the adopted Generalized Kelvin Model is adequate in describing the stress?strain relationship of asphalt binder at low temperatures.