A phase interpolation circuit including a first multiplexer, a second multiplexer, an interpolator and a duty-cycle repeater is provided. The first multiplexer receives a plurality of even order signals. The second multiplexer receives a plurality of odd order signals. The interpolator receives a first reference signal composed of one of the even order signals through the first multiplexer, and receives a second reference signal composed of one of the odd order signals through the second multiplexer. The interpolator divides a phase difference between the first reference signal and the second reference signal into a plurality of sub-phases according to a digital control signal, and selects one of the sub-phases to generate a differential input signal. The duty-cycle repeater adjusts the duty cycle of the differential input signal and accordingly generates a differential output signal with 50% duty cycle.