Electrical impedance in a partially molten gabbro was measured with the two-electrode method in the frequency range of 0.032 Hz to 10 kHz. Samples of different thicknesses were used to separate the bulk polarization effect from the sample-electrode interface polarization effect. The measurements show that both real and imaginary impedances increase linearly with increasing sample thickness. When the impedance data are extrapolated to zero thickness, the real impedance is as small as the experimental error, whereas the imaginary impedance has a finite value. This result indicates that the real impedance is mainly controlled by the electrical properties of the partially molten gabbro itself and that only small amounts of electrode interface polarization contribute to the imaginary impedance. After correction for the interface polarization effect, the present data were analyzed by the theoretical expression that describes the electrical impedance of partially molten rocks. The results show that frequency dispersion of electrical impedance in partially molten gabbro is associated with the polarization effect of ions in the partial melt.