Embodiments of this application provide a phase shifter and a base station antenna. The phase shifter includes a fixing frame, a phase-shifting stripline, and a sliding dielectric. The fixing frame includes a guide rail. The phase-shifting stripline is fixed on the guide rail. The sliding dielectric is slidably connected to the guide rail, and the sliding dielectric is separated from the phase-shifting stripline by the guide rail. The guide rail can guide movement of the sliding dielectric relative to the phase-shifting stripline, helping improve smoothness of the movement of the sliding dielectric relative to the phase-shifting stripline. Because the sliding dielectric is separated from the phase-shifting stripline by the guide rail, and during the movement of the sliding dielectric relative to the phase-shifting stripline, the sliding dielectric does not rub against the phase-shifting stripline.