An experimental study on the neutron irradiation induced thermal properties changes of various carbon fiber composites has been carried out using the High Flux Reactor of Petten. The investigated materials include: A05 (2D felt-type CFC), CX 2002U (2D felt-type CFC), DMS 678 (2D woven CFC) and N 112 (3D CFC). The irradiation temperatures range from 610 to 1030 degrees C and the neutron doses are between 0.8 to 1.8 dpa. This paper presents the experimental results on the neutron induced changes of the specific heat capacity, thermal diffusivity, and thermal conductivity.