The present relates to a fractional-N frequency synthesizer improving noise characteristics and a method thereof. The fractional-N frequency synthesizer includes a reference oscillator that generates a reference frequency signal; a sigma-delta modulator that generates a desired decimal value based on the reference frequency signal; a divider that divides a voltage controlled oscillation frequency signal; first to M phase/frequency detectors that detect a difference in phase and frequency between the reference frequency signal and the divided voltage controlled oscillation frequency signal; first to M charge pumps that are connected to each of the phase/frequency detectors in series and charges or pumps charge amount according to output signals from each of the phase/frequency detectors; a loop filter that controls the amount of supplied current based on output signals from the charge pumps to filter low-pass frequency components; and a voltage controlled oscillator that is oscillated in response to the output signal from the loop filter and generates voltage controlled oscillation frequency signals.