Abstract. In the present paper, we generalize the theory of quantitative homogenization for second-order elliptic systems with rapidly oscillating coefficients in AP W 2 (R d ), which is the space of almost-periodic functions in the sense of H. Weyl. We obtain the large scale uniform boundary Lipschitz estimate, for both Dirichlet and Neumann problems in C 1,α domains. We also obtain large scale uniform boundary Hölder estimates in C 1,α domains and L 2 Rellich estimates in Lipschitz domains.