A novel compact five-port waveguide power divider based on the single-ridge waveguide and three-ridge waveguide structure is proposed. It is realized by the coupling of the TE10 and TE30 modes. At the central coupling section, the single-ridge and three-ridge waveguides are used to constitute the conventional rectangular waveguide to reduce the sectional sizes. It consists of one input port, two output ports, and two isolated ports. For validation, a compact five-port power divider is designed, fabricated, and measured. The measured results show that, from 8 to 9 GHz, the return loss of the input port and output ports is higher than 18 dB, the isolation between the output ports is higher than 15 dB, the insertion loss is less than 0.3 dB, and the amplitude and the phase imbalance between the output ports are less than ±0.05 dB and ±1°, respectively. The simulated results basically agree with the simulations. Its sectional sizes are 1.1 λ × 0.4 λ which are more compact than most of the two-way isolated waveguide power dividers.