An experimental study on the effect of neutron irradiation on the properties of graphites and silicon carbides has been carried out using the Phenix reactor. The irradiation temperatures range from 420 to 540-degrees-C and the neutron doses are between 14 to 30 dpa. This paper presents the experimental results on the neutron-induced swelling, changes in thermal and mechanical properties of two different ultrafine grain isotropic polygranular graphites and two grades of silicon carbides.