There are a number of constitutive models for glassy polymers developed recently, attempting to combine all the important aspects of deformation of polymer glasses in a single constitutive model and thus be able to describe the behaviour of a material in the widest range, and under the various modes of loading and boundary conditions. However, a single constitutive model which can show accurately the nonlinear viscoelastic response under complex loading history, especially during unloading which polymers exhibit ‘enhanced recorvery’, yield drop and strain hardening behaviour, has never been reported before in the literature. The aim of the work is to extend the anisostructural model in the form developed earlier in the work of Chaikittiratana [2000] further such that it can describe more realistic yield peak and to include the feature of strain hardening after yield. It was found that the yield peak can be captured more realistically by assuming that the shear activation volumes should vary linearly across the discrete relaxation spectrum such that shorter relaxation times are associated with larger shear activation volumes. Furthermore, with this variation of shear activation volumes, the features of nonlinear viscoelastic creep-recovery, especially the ‘enhanced recovery’, effects are still in good agreement with the experimental data. The strain hardening feature was successfully implemented in to the existing anisostructural model by employing Edwards-Vilgis strain energy function and moderately good fit to the data was obtained.