We report Q-switched and mode-locked erbium-doped all-fiber lasers using ternary ReS2(1 x)Se2x as saturable absorbers (SAs). The modulation depth and saturable intensity of the film SA are 1.8% and 0.046 MW/cm2. In Q-switched mechanism output, the pulse was centered at 1531.1 nm with maximum pulse energy and minimum pulse width of 28.29 nJ and 1.07 μs, respectively. In mode-locked operation, the pulse was centered at 1561.15 nm with pulse width of 888 fs, repetition rate of 2.95 MHz, and maximum pulse energy of 0.275 nJ. To the best of our knowledge, this is the first report on the mode-locked Er3+-doped fiber laser using ternary transition metal dichalcogenides. This work suggests prospective 2D-material SAs can be widely used in versatile fields due to their attractive optoelectronic and tunable energy bandgap properties.