The second-order nonlinear optical polarizabilities of a series of substitutedcinnamonaldehyde derivatives using the CNDO/S-CI method and Perturbation theory wereCalculated and the structure dependence of their nonlinear optical properties was studied. TheresultS reveal that this kind of compounds have fairly large second-order POlarizabilities.Morever, there is close relation between the best structures and the high values of β. So weconsider that this series of compounds are worthy of being studied further.