We report, for the first time to our knowledge, on a single-mode millijoule-level 100-nanosecond Er-doped fiber laser operating near 1550 nm. The system features a newly developed 35-μm-core Yb-free double-clad Er-doped fiber based on P(2)O(5)-Al(2)O(3)-SiO(2) glass matrix and produces pulses with energy as high as 1 mJ at repetition rates of 1-10 kHz.