A novel multi-wavelength erbium-doped fiber ring laser is presented. Mach-Zehnder (M-Z) interferometer is used as comb filter and with an interlevel and composite cavity to selecte the wavelengths. The stable three-wavelength outputs with 0.8-nm wavelength span and 0.1-nm linewidth are obtained at room temperature. Without cooling the gain medium in liquid nitrogen or using gratings and complex, expensive devices, this fiber laser has the advantages of being simple and easily attainable at a low cost.