Alloy surfaces of Cu-Au (001) and (110) are prepared by a vaporization and heating method, and are investigated by LEED. Surface structures of the hexagonal and c(2×2) typcs on the (001) surface, and (1×2), (∼4×∼1), c(3×∼1) and (2×2) on the (110) surface, are obtained by changing the mean surface composition, orresponding tructurdl models are given. In-depth distribution of atomic concentration at the Cu-Au alloy surface, after depositing gold onto the surface to the thickness of 3.3 nm with subsequent heat treatments, is presented on the basis of Fick's second law, using diffusion coefficients given by kubashewski. Theoretical treetmcnt of the surface composition change caused by annealing is compared with experiment with AES on surfaces of Cu-Au alloys over a wide composition vangc of the Cu-rich side. Surface composition given by the thoretical in-depth profiles is in agreement with that obained by experiment.