Segregation of substrate Al on thin Zr film, Zr/Al/Al system was investigated by heating the specimen in a UHV chamber. Dual-cathode magnetron-sputtering source was used for deposition of Zr film as well as thin Al film to avoid aluminum oxide formation at Zr/Al interface. Al segregates on Zr film surface at 730 K. It was found that oxide-free interface between film and substrate is important for segregation in Al system. The diffusion coefficient calculated for surface segregation and inter-metallic compound showed that the grain boundary diffusion and bulk diffusion are very close in Zr/Al/Al system. Hence, it is important to control specimen heating to cause surface segregation by grain boundary diffusion. (C) 2003 Elsevier B.V. All rights reserved.