This paper describes the design and operation of a stable single-longitudinal-mode medium-power multiwavelength fiber ring laser at room temperature. Single-longitudinal-mode oscillation was achieved by using an unpumped polarization-maintaining erbium-doped fiber inside the cavity as a saturable absorber. To investigate the function of the saturable absorber, erbium-doped fibers with different erbium concentrations and lengths were used. The output characteristics of the laser were studied using a scanning Fabry-Perot spectrum analyzer of resolution and an optical spectrum analyzer of resolution . The total output power of the laser obtained was more than . The minimum separation between lasing wavelengths for stable single-longitudinal-mode oscillations, number of lasing lines, tunability, and maximum available output power were also explored.