During the few past years the development of natural fiber composites for structural applications has gained the momentum. Mainly the efforts in development of these materials were focused on the composites with synthetic matrices. But most recently several bio-based resins (Tribest, EpoBioX etc.) have been introduced, allowing production of whole bio-based composites. The latest results demonstrated that these composites are comparable with glass fiber reinforced polymers in terms of stiffness. However due to variability of fiber properties and limited filament length it is complicated to arrange and control fiber alignment in composites as well as ensure stable, predictable composite properties. Therefore, another type of reinforcement with natural origin has caught attention of researchers – Regenerated Cellulose Fibers (RCF). These fibers are continuous with constant, reproducible cross-section and properties but with one significant disadvantage - they exhibit highly non-linear behavior. Thus, this reinforcement should be treated as material with time-dependent properties. Schepary developed model for time-dependent materials. This model has been successfully applied to short fiber (natural and synthetic) and long synthetic fiber composites. However, in order to apply this model, large number of time-consuming tests on studied composites must be performed. Therefore, our objective is to improve this model in such a way that only input of properties of constituents is required to predict behavior of material with any composition. Visco-elasticity and viscoplasticity has been analyzed by performing creep tests at different time steps and stress levels, and extent of damage is evaluated by performing stiffness degradation tests of fibers, matrix and composite.