We demonstrated a 2-μm passively mode-locked nanosecond fiber laser based on a MoS2 saturable absorber (SA).Owing to the effect of nonlinear absorption in the MoS2 SA,the pulse width decreased from 64.7 to 13.8 ns with increasing pump power from 1.10 to 1.45 W.The use of a narrow-bandwidth fiber Bragg grating resulted in a central wavelength and 3-dB spectral bandwidth of 2010.16 and 0.15 nm,respectively.Experimental results show that MoS2 is a promising material for a 2-μm mode-locked fiber laser.