Results of low- and high-frequency modulation of laser beam, propagating both in the direction of optical axis and along three crystallographic axes in Fe-doped KNb03 crystal, are presented. It was found, that the high-frequency electro-optical constants of Fe:KNb03 are: r33 = (5353) pm/V, r13 = (21±3) pm/V, and r51 = (88±11) p d V . The difference between high- and low-frequency values is about 20% and this is in good accordance with known data for nominally pure crystal. We found also, that there was no twinning effect in this crystal under the electrical fields up to 2.5 kV/cm. The half-wave voltage was only 800 V at the wavelength of 633 nm in a longitudinal configuration of modulator. We measure also that bandpass of light modulation in Fe:KNb03 is equal to at least 6 MHz. In our experiments we also determined the speed of acoustic waves, created in the crystal by inverse piezoelectric effect, when fast HV electrical pulse is applied to it, these values are vl=(56001100) d s and v2=(6400±100) m/s along Oz and Ox axes correspondingly.