c-axis thermoelectric power (TEP)Scof stage-2 graphite intercalation compound with iodine monobromide (IBr-GIC) was measured below the room temperature, and the calculation was carried out by our theory. The major part ofSccomes from the diffusion TEPSc-d. However, a slight deviation exists betweenSc-dand the experimental resultScand it can be removed in consideration of phonon drag TEPSc-p. This situation was different from the case of graphite intercalation compound with iodine monochrolide (ICI-GICs). Above the room temperature, we attempted to measure the TEP of stage-2 IBr-GIC. It shows the phase transition similar to the case in ICI-GICs.