ABSTRACTJanus transition metal dichalcogenides (TMDCs) type two-dimensional materials have been widely studied because of their unique asymmetrical structures and properties. In the preparation of Janus TMDCs, replacing the top layer S atoms of MoS2 with H atoms could yield unique Janus MoSH, which has been scarcely reported. In this work, the electronic, mechanical and piezoelectric properties of Janus MoSH are systematically studied using first principles calculations for the first time. The band structure of Janus MoSH is of metallic nature with two bands crossing the Fermi level. This material has a stable structure, and the Poison ratio ν > 1/3 indicates the good ductility. The relatively higher piezoelectric coefficients, e11 of −4.27 × 10−10 C/m and d11 of −5.09 pm/V for Janus MoSH, compared with the typical piezoelectric semiconductor materials MoS2 (3.64 × 10−10 C/m and 3.73 pm/V, respectively) may reflect suitable piezoelectric effect in the former. The above calculations may show that Janus MoSH would be potentially adopted as efficient sensors and piezoelectric components.