Film bulk acoustic wave resonator (FBAR) filters are promising for the mobile communication devices. Frequency switchable filters are suitable for selecting the vacant frequency bands. Usual polarity unidirectional single layer resonator excites fundamental mode whereas polarity inverted double layer resonator excites second mode. In this study, we considered that polarity inverted structure is easily obtained by applying DC field, which is less than coercive field of BaTiO3, to two-layered BST/BaTiO3 epitaxial films. During the application of -36 V, the two-layered resonator excites fundamental mode. On the other hand, during the application of +36 V, the resonator excites second mode. These results show frequency band switching by DC field.