A 1 x 1 power divider based on the four-branch single-mode waveguide is proposed and fabricated. The proposed structure has one beam separator and two beam expanders in the branching region. The uniform output power distribution can be obtained by adjusting the sizes of the beam separator and the beam expander. The measured powers of four output ports are uniform for both TE and TM modes within the difference of 0.3 dB, The effects of the beam separator and the beam expander on the power dividing ratio and the scattering loss of the proposed device are also discussed.