Effective thermal conductivities in four different packed beds are experimentally studied in this paper, namely two random graphite packed beds with porosity ?=0.40 and ?=0.35, a simple cubic (SC) graphite packed bed and a random stainless steel packed bed. It is found that the effective thermal conductivity of all packed beds has a downward trend as the wall is approached. Based on the effective thermal conductivity distributions, the near wall region can be defined within four pebble diameters from walls for random packed beds and one pebble diameter for SC packed beds. As a result of wall effect, the effective thermal conductivities in the near wall regions are generally smaller than those in the bulk regions at the same temperature. It is found that the ZBS correlation gives best predictions in bulk regions and in near wall regions with the proper empirical parameter selected.