We report a systematic study of the etching of MoSs crystals by using XeF2 as a gaseous reactant. By controlling the etching process, monolayer MoS2 with uniform morphology can be obtained. The Raman and photoluminescence spectra of the resulting material were similar to those of exfoliated MoS2. Utilizing this strategy, different patterns such as a Hall bar structure and a hexagonal array can be realized. Furthermore, the etching mechanism was studied by introducing graphene as an etching mask. We believe our technique opens an easy and controllable way of etching MoS2, which can be used to fabricate complex nanostructures, such as nanoribbons, quantum dots, and transistor structures. This etching process using XeF2 can also be extended to other interesting two-dimensional crystals.