Inadequacies in the temperature measurement within the moving bed have hindered a thorough understanding of the processes occurring within rotary kilns. A new measuring system, consisting of thermocouple arrays, a radio-transmitter, a radio-receiver and a computer monitor is introduced in this paper. With it, the 3D temperatures within the moving bed, as well as the temperatures of the freeboard gas and the kiln wall, can be measured and saved automatically. Experiments with sand on a co-current pilot kiln demonstrated that, in the passive layer of the moving bed, the temperatures were approximately constant in the circumferential direction. In the radial direction, however, large temperature difference was observed within the bed near the feed end of the kiln, and the difference became smaller as the bed went progressed through the kiln. This temperature measuring system can be used to obtain data over a wide range of operating conditions for use in engineering design. The obtained results may give new thoughts in theoretical modeling of heat transfer within the moving bed of rotary kilns. (C) 2010 Elsevier B.V. All rights reserved.