A novel switchable dual-wavelength erbium-doped fiber (EDF) laser is demonstrated. The wavelength selection element consists of two fiber Bragg gratings (FBGs), a polarization controller (PC) and a 3 dB coupler forming a Sagnac loop inserted with two FBGs. We study the effect of coupling ratio on filtering performance in this paper. By adjusting PC, we can change the wavelength-dependent loss, and then using nonlinear polarization rotation effect to suppress the mode competition caused by the homogeneous broadening of EDF, we obtain single- and double-wavelength laser outputs. At room temperature, under 200 mW pump power, dual-wavelength laser is achieved, and the center wavelengths are 1545.34 nm and 1548.20 nm, respectively. The peak power values are –13.36 dBm and –14.58 dBm, and side mode suppression ratios (SMSRs) are 41.10 dB and 39.88 dB, respectively. Within two hours, the maximum fluctuation of peak power is less than 0.7 dB, which shows that the demonstrated fiber laser is stable. Moreover, by adjusting PC, singel-wavelength laser output is obtained, the peak power is –6.27 dBm or –5.45 dBm, and SMSR is 40.03 dB or 39.96 dB at 1545.34 nm or 1548.20 nm, respectively.