Surface segregation phenomena of Pb in Al-100 mass-ppm Pb foil during annealing at 540-610 degreesC in three environments, open air, argon and vacuum (about 0.1 Pa), were observed by RBS and TEM. RBS spectra showed most of the lead segregated within a depth of 150 nm of the surface. The degree of surface segregation of Pb in the annealed foils was as follows: open air > argon > vacuum atmosphere. In the open air and argon atmospheres, the surface segregation increased with annealing time but it diminished with annealing time in a vacuum. TEM observations revealed that most of the Pb element in the foils segregated not to the aluminum surface but to the oxide film just above this surface formed by annealing treatment, although the compositions of lead, aluminum and oxygen were different depending on the position in the oxide film. The competition between the thermal diffusion of lead though the aluminum bulk and the vaporization of lead at the oxide film surface results in the surface segregation of lead.