The ageing of a new family of thermoplastic elastomers from blends of natural rubber and polyethylene was studied using thermal treatments at 65degrees, 80degrees and 90degreesC. The effects of including various stabilizers and dynamic vulcanization were also investigated. The results of UV ageing in a weatherometer and sunlight ageing of the same samples were compared. Thermal ageing of the blends of two polymers caused the tensile properties to deteriorate, especially at longer times or higher temperatures of ageing. The tensile strength and modulus of dynamically vulcanized blends, which registered higher tensile properties, increased in the initial stage on thermal ageing before a final drop. When an antioxidant for rubber or heat or light stabilizer for polyethylene was added, thermooxidative stability was increased. Dynamic mechanical properties also indicated changes due to ageing. UV and sunlight ageing of the samples revealed that the antioxidant for rubber improved the properties. The results are explained in terms of crosslinking, degradation and crystallinity of the blends. No cracking was observed on the surfaces of the aged samples, even under prolonged periods of ageing and on extending the specimens under the microscope.