Disclosed is an apparatus and method for calibrating and compensating for distortion of an output signal to an antenna in a mobile communication system with a smart antenna array. A calibration signal generator generates an extended Walsh code by extending a Walsh code used in the mobile communication system, and generates a calibration signal in synchronism with a Walsh code synchronization signal of the mobile communication system. A mobile communication signal generator generates a traffic signal for forming a beam pattern to a position of a mobile terminal in communication. A multiplier multiplies an error compensation value by an output signal of the mobile communication signal generator. An adder adds an output of the multiplier to an output signal of the calibration signal generator. An RF block for up-converting an output signal of the adder into an RF band signal, provides the up-converted RF band signal to the antenna array, extracts part of the signal provided to the antenna array, and feeds back the extracted signal component. An error calibration and compensation value calculator calibrates an error of the antenna array from the feedback signal, calculates a compensation value for compensating for the error, and provides the compensation value to the multiplier.