The back-molding of continuous fiber-reinforced thermoplastics – so-called composite sheets – combines the benefits of a high degree in design freedom by injection molding and the high mechanical performance of the semi-finished composite sheets. The integration of the forming process of the composite sheet into the injection molding process results in high-functionalized lightweight structures in adequate cycle times. Consequently the opportunity of a high-volume production for those composite parts exists which is attractive for applications in the automotive industry. During their operation time the composite structures are exposed to many different environmental influences, like mechanical loads, dampness, temperature changes or ultraviolet radiation. The interaction with the environmental conditions leads to the aging of the polymer and results in changes of the material properties. Strength losses, embrittlement, degradation of the molecular weight or optical changes are some examples and may induce a prematurely failure of the composite parts. To be able to predict the life time of those lightweight components, the influence of the aging process on several material properties has to be known. Hence, the environmental aging of back-molded composite sheets will be investigated and the changes of the material properties will be characterized.