A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at 2.0 mu m for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, 24.2 mu J, and 80 W, respectively. The results are distinguished from other two-dimensional materials-based 2.0 mu m PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the 2.0 mu m spectral range.