We have demonstrated a new scheme of harmonically mode-locked fiber laser utilizing an all-fiber acousto-optic modulator, which is composed of a two-mode fiber, as an active mode-locker. The harmonically mode-locked lasing occurs when a harmonic frequency of the modulator driven frequency matches with one of the harmonics of the cavity modes at the least common multiple frequency value. The mode-locked laser pulses were obtained at the 7th harmonics of the cavity's fundamental mode frequency. (C) 1998 Elsevier Science B.V.