Multi-wavelength fiber ring laser based on the semiconductor optical amplifier (SOA) with sampled fiber Bragg grating (SFBG) in a Sagnac loop interferometer as the wavelength-selective filter is proposed. Four lasing wavelengths with 1.8 nm spacing have been generated stably at room temperature. The proposed laser has the advantages such as removal of the high-cost circulator, flexibility in channel-spacing tuning, and simple all-optical fiber configuration, which has potential applications in high-capacity wavelength-division-multiplexed (WDM) systems and mechanical sensors.