Amplification characteristics of erbium‐doped optical fiber amplifier have been investigated using femtosecond soliton pulses with various wavelengths. Soliton trapping is not observed for 210 fs input pulses at 1.535 &mgr;m but the soliton self‐frequency shift occurs along with the pulse‐width narrowing. When the input pulse width is 470 fs, the soliton pulse is amplified by the optical gain at 1.535 &mgr;m, where the gain bandwidth is broader than the bandwidth of the input pulse. Amplification characteristics at other nonresonant wavelengths are also investigated using a femtosecond soliton pulse.