The disclosure relates to an AC LED dimmer and dimming method thereof. The AC LED dimmer includes a rectifier receiving AC voltage from an AC voltage source and full-wave rectifying the AC voltage; a direct current (DC)/DC converter receiving the full-wave rectified voltage from the rectifier, generating a full-wave rectified stepped-up voltage, and generating a pulse enable signal; a pulse width modulation controller receiving the full-wave rectified stepped-up voltage and generating a pulse width modulation signal to dim an AC LED in response to the pulse enable signal; a switch driving the AC LED under control of the pulse width modulation signal, and an electromagnetic interference (EMI) filter to be connected between the AC voltage source and the switch to eliminate electromagnetic interference from the AC voltage source. Accordingly, the dimmer can perform an efficient and linear dimming function and suppress harmonics.