The present invention relates to a low voltage drop out regulator and method for improving power supply rejection ratio thereof. The low voltage drop out (LDO) regulator comprises a voltage buffer for receiving an input voltage containing a DC component of a first level and an AC component, converting the input voltage to output a converted voltage, the converted voltage having a DC component of a second level lower than the first level and an AC component following that of the input voltage; a control stage having a first amplifier applied with the converted voltage; and an output stage having a power transistor connected with an output of the first amplifier of the control stage, the power transistor being applied with the input voltage and being controlled by the control stage to output an output voltage with a third level. The power supply rejection ratio is improved and the AC perturbation is eliminated because both of the input voltage and the converted voltage contain the DC component.