It is well known that asphaltic materials present complicated viscoelastic behaviour that is significantly affected by the rate of loading and time as well as by temperature conditions. To improve accuracy in the analysis and design of asphaltic materials and pavement structures, the viscoelastic constitutive model has been considered by many studies. However, abundant experimental observations have presented nonlinear response of asphaltic materials at certain levels of stress and strain, and the nonlinear behaviour is not considered in the current pavement design methods. This study develops testing- Analysis methods to rigorously define the stress-dependent nonlinear viscoelastic material characteristics at various stress levels. To this end, Schapery's nonlinear viscoelastic model is employed to characterize the nonlinear viscoelastic behaviour of asphaltic materials in two different length scales, i.e., mixture scale and component scale. The test and analysis results discussed in this paper provide a better understanding and identification of the true mechanical behaviour of asphaltic materials in pavements.