Light confinement to sub‐wavelength scales is actively studied for nanophotonic applications because it gives rise to intriguing optical properties with enhanced light‐matter interaction. Herein, an ultrathin exciton–polariton waveguide based on a WS2 multilayer is proposed for sub‐wavelength light guiding. A WS2 waveguide supports guided exciton–polariton modes even with a few tens of nanometers of thickness. It is theoretically confirmed that the WS2 waveguide has significantly lower propagation loss than a plasmonic mode, although its thickness may be similar to that of a plasmonic waveguide. By injecting white light into a fabricated WS2 waveguide, light guiding is experimentally demonstrated through a 20 nm thick WS2 waveguide. Notably, this study integrated the WS2 waveguide with a WSe2 monolayer to demonstrate the coupling of monolayer emission to the polariton waveguide. The results suggest that WS2 multilayers provide a novel material platform with potential for nanophotonic applications, including ultrathin optical integrated circuits. An exciton–polariton waveguide based on the WS2 ultrathin film (20 nm) is demonstrated. Theoretically and experimentally, the optical properties of the WS2 waveguide are verified, and the advantages of the WS2 waveguide are confirmed through comparison with other waveguides. Finally, the possibility of application is also shown by coupling of WSe2 exciton emission to the WS2 waveguide.