We propose and demonstrate a simple configuration of wavelength-tunable fiber laser made up of a tunable band-pass filter, a Sagnac loop refiector, and a Fabry-Perot laser diode. Based on the self-seeded operation, the proposed fiber laser can obtain a single-longitudinal-mode output in the wavelength tuning range of 1544.69-1563.39 nm with tuning step of 1.34 nm. The performances of output power (>-9 dBm), optical side-mode suppression ratio (> 65.5 dB), and power and wavelength stabilities are well exhibited. We propose and demonstrate a simple configuration of a wavelength-tunable fiber laser made up of a tunable band-pass filter, a Sagnac loop refiector, and a Fabry-Perot laser diode. Based on the self-seeded operation, the proposed fiber laser can obtain a single-longitudinal-mode output in the wavelength tuning range of 1544.69-1563.39 nm with a tuning step of 1.34 nm. The performances of output power (> -9 dBm), optical side-mode suppression ratio (> 65.5 dB), and power and wavelength stabilities are well exhibited.