An apparatus and method for a vector interpolation of an ultrasound image are provided. The apparatus includes a probe, beam former, demodulator and interpolation processor. The probe converts an electric signal into an ultrasound signal, transmits the ultrasound signal to an object, and converts a reflected ultrasound signal from the object into a reflected electric signal. The beam former forms a receive-focused signal based on the electric signal converted from the reflected ultrasound signal by the probe. The demodulator demodulates the receive-focused signal for forming I data corresponding to in-phase components and Q data corresponding to quadrature-phase components. And the interpolation processor performs a vector interpolation with 1:M weighting (M is a natural number) between different complex-valued signals, based on the I data and the Q data.
