Provided is a multi-band amplifier and a method of amplifying a multi-band. The multi-band amplifier includes a wireless signal input terminal into which a first frequency band signal and a second frequency band signal are input, a first impedance matching part connected to the wireless signal input terminal and configured to match an input impedance in a first frequency band, a second impedance matching part connected to the wireless signal input terminal and configured to match an input impedance in a second frequency band, a common source amplifier to which the first impedance matching part and the second impedance matching part, and a common gate amplifier connected to the common source amplifier. Accordingly, performance degradation can be reduced in comparison with a conventional amplifier, broadband amplification as well as narrow band amplification can be performed, and an amplification gain can be adjusted.