In the first phases of the development of thermoelectric systems, such as the thermoelectric generators, when the thermal design is carried out, the most important parameters affecting the performance are the thermal resistances of the components. This paper focusses on the thermal contact resistance (TCR), analyzing the influence of aging and temperature on different thermal interface materials (TIM), i.e., thermal paste, graphite and indium. In previous papers, TCR has been studied depending on parameters such as surface roughness, bonding pressure, thermal conductivity and surface hardness. However, in thermoelectric applications, a relevant aspect to consider when choosing a TIM is aging due to thermal stress. The exposure of this type of materials to high temperatures for long periods of time leads to deterioration, which causes an increase in the thermal contact resistance which impairs the conduction of the heat flow. Therefore, there is a need to study the behavior of thermal interface materials exposed to temperatures typical in thermoelectric generators, to make a correct selection of the TIM. It has been observed that exposure temperatures of around 180 °C induce a significant increase in the thermal impedance of the three TIM's under study, although this effect is much more relevant for the thermal paste. The contact comprising steel, thermal paste and ceramic presents a 300% increase in the thermal impedance after 70 days of aging, whereas that exceeds 185% for the contact of aluminum, thermal paste and ceramic. In the tests with exposure temperature of 60 °C, there is no observed decrease in the thermal impedance.