A waveguide includes: a dielectric including two surfaces, an electric field intersecting with the two surfaces; metal-plating layers coating the two surfaces of the dielectric, the electric field intersecting with the two surfaces; and a protective layer coating a periphery of the dielectric including the two surfaces coated with the metal-plating layers. A wireless transmission system includes: a sender configured to send a high-frequency signal; and a receiver configured to receive the high-frequency signal. The waveguide is used as a waveguide configured to transmit the high-frequency signal between the sender and the receiver in the wireless transmission system.