We study the electronic structures and the magnetoelectric (ME) effect in Fe/KNbO3 superlattices theoretically. The interior KNbO3 layers in superlattices with the NbO2 terminations are insulating. While they are metallic for the KO terminations. The interface Fe Nb and Fe-O bonds induce large magnetic moments on Nb and O atoms. The magnitude of the induced magnetic moments is related to the polarization direction of the KNbO3 layers. We obtain a large ME effect in NbO2-terminated superlattices. However the ME effect is negligible in KO-terminated superlattices due to the opposite sign of variations of magnetic moments on O and Fe at two interfaces. (C) 2014 Elsevier B.V. All rights reserved.