On die termination circuit and method for calibrating the same includes a external resistor connected to a first node, a plurality of calibration resistors connected to a second node, the plurality of calibration resistors being turned on/off in response to a calibration code set, a current mirror configured to mirror currents of the first node and the second node and a code generator configured to generate a calibration code set according to the mirrored currents. In accordance with a method for calibrating an on die termination circuit of the present invention, the method includes a step of mirroring a current of a first node connected to an external resistor and a current of a second node connected to a plurality of calibration resistors and a step of generating a calibration code set according to the mirrored currents.