The effects of orientation of turbulence promoting ribs in the internal cooling air passage on the film cooling performance of outer surface of gas turbine blades have been studied experimentally. Both the adiabatic film cooling effectiveness and the heat transfer coefficient downstream of the film-cooling hole of a flat plate were measured for two different orientations of the turbulence promoting ribs. It is found that the adiabatic film cooling effectiveness and heat transfer coefficient on the external surface are considerably affected by the inversion of the rib orientation in the internal passage. The film cooling performance is evaluated in terms of the net heat flux reduction and the net surface temperature reduction, both of which are calculated from the measurement of adiabatic film cooling effectiveness and heat transfer coefficient. The evaluation of these quantities has clarified the effects of the internal cooling structure on the film cooling performance.