A multi-band low noise amplifier capable of operating in a plurality of band modes includes a plurality of input amplifiers respectively corresponding to the plurality of band modes and an output amplifier. Each input amplifier includes a receiving port for receiving a corresponding input signal in the band mode. The output amplifier includes at least a lowest-impedance port being a lowest-impedance node of the multi-band low noise amplifier and an output port for outputting the input signal processed by the output amplifier. The output amplifier is coupled to the plurality of input amplifiers at the lowest-impedance port.