Abstract: Mid-infrared region ranging from 2.5 μm to 25 μm covers absorption lines of most molecules and multiple atmospheric windows. The ultrafast lasers operating in this waveband have vast applications in many fields. In recent years, significant progress has been made in the area of mid-infrared fiber-based ultrafast lasers in terms of long waveband emission and ultrafast pulse generation, which enables many unexplored reseaches and novel applications. In this paper, we reviewed the development of mid-infrared ultrafast fiber lasers over the last decade. Starting with the fiber materials and the gain medium used for mid-infrared emission, we focused on the current mode-locking methods and their representative progress for mid-infrared fiber lasers including nonlinear polarization rotation, saturable absorbers and frequency shifted feedback technique. Then we briefly discussed the mid-infrared pulse post-modification and typical applications including few-circle pulses and supercontinuum generation. Finally, the critical challenges the mid-infrared ultrafast fiber lasers are currently facing and the possible routines for further development were summarized.