Summary: We develop a posteriori error estimator for two-dimensional adaptive boundary element method. The nodal errors of the state variables (displacements and tractions) are estimated based on the difference of two solutions, one from the original boundary elements solution, and the other from interpolation of the original solution. The \(L_2\) norm is employed to compute local and global percentage errors. An \(h\)-version adaptive boundary element method has been implemented, and three numerical examples are used to verify the effectiveness of the error indicator.