A method of measuring a bio signal using a bio signal measuring apparatus includes: positioning electrodes included as part of the bio signal measuring apparatus to contact a surface of an examinee； switching an impedance measurer included as part of the bio signal measuring apparatus and including a voltmeter and a current source； measuring a first impedance value of the examinee while operating the impedance measurer according to a first mode； switching the impedance measurer to a second mode； measuring a second impedance value of the examinee while operating the impedance measurer according to a second mode； and obtaining bio impedance of the examinee based on the first and second impedance values and an internal impedance of the current source.
