The suppression of intensity noise in a 1.5 μm distributed Bragg reflector (DBR) single-longitudinal-mode fiber laser using optoelectronic feedback was reported. By analyzing the transfer function from the pump disturbance to the output power fluctuation, it was found that the phase of the fiber laser has a 180° phase mutation at the relaxation oscillation frequency. Therefore, a first-order phase-shifting network, which can provide a 45° lead phase at the relaxation oscillation frequency to compensate for the phase mutation at that frequency, was designed and constructed based on an existing commercial proportional integral (PI) control circuit. With the designed feedback control system, the relaxation oscillation peak of the laser was reduced from -95 dB/Hz to -125 dB/Hz, the suppression amplitude was as high as 30 dB. The suppressed fiber laser is expected to play an important role in applications such as precision measurement.