A switchable and tunable ytterbium-doped fiber ring laser (YDFL) is reported and demonstrated. Employing a Sagnac loop mirror fabricated by an 85-cm-long polarization-maintaining fiber (PMF), the proposed YDFL can operate with stable dual-wavelength lasing or tunable single-wavelength lasing around 1 064 nm. Both stable dual-wavelength lasing and tunable single-wavelength lasing are achieved by adjusting a polarization controller in the Sagnac loop mirror. The experimental results show that the output of the proposed fiber laser with two different operation modes is rather stable at room temperature.