In this paper, we prove two unique continuation results for second order elliptic equations with Robin boundary conditions on C 1,1 domains. We first prove a sharp vanishing order estimate of Robin problems with Lipschitz coefficients and differentiable potentials. This is comparable to the estimates for the interior case in [2, 24] and the Dirichlet case in [3]. Furthermore, it generalizes the result for the "Robin eigenfunctions" in [25], which dealt with the case with constant potentials. The second result in the current paper is the unique continuation from the boundary, which generalizes the one in [1] for Laplace equations with Neumann boundary conditions. Our result also improves [8] as we remove a geometric condition.