Thermally conductive modified materials are being increasingly applied in different fields of industry. Some of these applications have long lifecycles of 10 years or above. Due to that it has to be ensured that the thermal conductivity of the used materials is remaining at least about the same period of time. Usually the increase of the thermal conductivity is achieved by adding thermally conductive filler materials. Carbon or ceramic fillers are the most common types. In the last years several investigations in the field of thermally conductive materials analyzed the influence of different filler materials, filler content and processing conditions. Also the aging behavior of commonly used polymers is widely described. But studies on the aging behavior of thermally conductive composites are still missing. Existing studies on fiber reinforced composites are just poorly comparable. Besides the fact that they differ in terms of filler type and filler content, these investigations usually focus on mechanical rather than thermal properties. To fill this gap different matrix materials are compounded with typical ceramic and carbon based fillers. After processing in injection molding the specimen are subjected to artificial aging cycles and their thermal conductivity is determined. Finally the results are discussed according to several aging based changes in the material, like cristallinity, moisture, filler-matrix interaction or thermo oxidative degradation using microscopy and thermal analysis .