Monopulse slot antenna arrays based on substrate integrated waveguide (SIW) are proposed for the application of 60 GHz monopulse tracking systems in this paper. The sum-difference monopulse comparator can provide a high amplitude and phase balance over wide frequency band and no phase delay technique is required for the difference channel. Resonant slot antennas are adopted as the radiating elements since they can be integrated with the sum-difference monopulse comparator in a single layer with a compact size. Two monopulse arrays with 2 × 4 and 4 × 4 slot elements are designed, fabricated, and measured. Measured results show that the proposed antenna arrays have wide bandwidth covering the unlicensed 60-GHz band. The peak sum beam gain is 13.85 dBi for the 2 × 4 element array and 16.24 dBi for the 4 × 4 element array. The peak difference beam gain is 11.20 dBi for the 2 × 4 element array and 12.11 dBi for the 4 × 4 element array and the maximum null depth can reach -40 dB.