The high-temperature heat transfer characteristics of the hot flow stream over a sudden-expansion with cold air uniformly injected from a porous base was investigated. The heal transfer coefficient increased with increasing inlet temperature and Reynolds number, but decreased with increasing injection rate of the cooling air. The local Nusselt number was affected by the Reynolds number at the inlet in the whole flow field except near the step (X/H < 4). The local Stanton number, however, was insensitive to the Reynolds number in the recirculation zone. After the recirculation zone, the local Stanton number was affected by the Reynolds number, although to a lesser extent than that of the Nusselt number.