Thermal barrier coatings consisting of ZrO_2-8wt%Y_2O_3 and NiCoCrAlY bond coat on a Ni base superalloy were used as test specimens. The indentation fatigue tests were conducted before and after thermal exposure test. The thermally grown oxide (TGO) layer increases with increase of thermal exposure time up to 200h. The interfacial damage was observed using scanning electronic microscope and digital microscope. The debonding and spalling of ceramic top coat occurred in the specimens thermally-exposed for 200h.