A new e-o waveplate is reported. Compared with ordinary e-o modulators, this device can control not only the phase -difference between o-beam and e-beam, but also the direction of the main axis of the waveplate, i. e. to change the ratio of amplitude of o-beam and e-beam.Hence we can get any states of polarization from one state of polarization using ths device. It can also be used as an e-o rotator.