We describe a polarization-maintaining (PM) λ/4-shifted DFB Er-doped fiber laser (EDFL), in which optical pulsation effects caused by Er3+ ion-pairs were successfully removed by co-doping erbium fiber with 12wt% aluminum. Stable CW operation was realized at a pump power of 100mW. The laser exhibited single longitudinal-mode oscillation with a single polarization. The output power, linewidth of the longitudinal mode, and RIN at the relaxation oscillation frequency were 0.5mW, 82kHz, and -79dB/Hz at a pump power of 100mW, respectively. Stable operation was also obtained at a pump power of 140mW, where the above values were improved to 0.8mW, 43kHz, and -92dB/Hz, respectively.