c-axis thermoelectric power (TEP) S-c of 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 of S-c comes from the diffusion TEP Sc-d. However, a slight deviation exists between Sc-d and the experimental result S-c and it can be removed in consideration of phonon drag TEP Sc-p. This situation was different from the case of graphite intercalation compound with iodine monochrolide (ICl-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 ICl-GICs.