A tunable and switchable dual-wavelength Er-doped fiber ring laser using simultaneously forward and backward amplified spontaneous emissions is proposed and demonstrated experimentally at room temperature. A polarization-maintaining fiber Sagnac interferometer is used as a comb filter. This laser has eleven different output modes in the range of 1559–1566nm that can be switched flexibly from one to another. Single- and dual-wavelength lasers with a 3-dB linewidth of 0.7nm and optical signal-to-noise ratios of more than 28dB have a small tunable range. Spacing of dual-wavelength laser can be changed from 1.8nm to 0.8nm with the wavelength׳s increment. The laser shows good wavelength and peak power stabilities.