A phase interpolator including a phase interpolation circuit, a plurality of low pass filtering channels, and a multiplexing circuit is provided. The phase interpolation circuit receives a first clock signal and a second clock signal and accordingly performs an interpolation operation to generate an output clock signal. The low pass filtering channels respectively have an output terminal and an input terminal that is coupled to the phase interpolation circuit to receive the output clock signal. Each of the low pass filtering channels includes a switch and a capacitor which are coupled to a common node as the output terminal. The multiplexing circuit has a plurality of input terminals respectively coupled to the output terminals of the low pass filtering channels. The multiplexing circuit selects an input signal received from one of the low pass filtering channels as a phase interpolation signal according to a selecting signal.