A low-voltage operational amplifier includes a differential amplifying stage, an output amplifying stage and a compensation stage. The differential amplifying stage amplifies a difference between a first signal and a second signal that constitute a differential pair using an input pair of NMOS transistors, and outputs an amplified first signal and an amplified second signal. The output amplifying stage amplifies a difference between the amplified first signal and the amplified second signal using an input pair of PMOS transistors, and outputs a first output signal and a second output signal that constitute a differential pair. The compensation stage receives the amplified first signal, the amplified second signal, the first output signal, and the second output signal, and reduces a settling time of the first output signal and the second output signal.