Bacteria regulate stress-response transcription using two-component systems to adapt to environmental changes. In Bacillus subtilis, the Css two-component system is responsible for counteracting envelope stress caused by heat, protein misfolding, and peptidoglycan stress. This envelope stress is directly recognized by the extracytoplasmic domain of CssS (CssS-ECD). As preliminary studies to understand the stress-sensing mechanism of CssS, CssS-ECD was expressed, purified, and crystallized. Diffraction data of CssS-ECD were collected at a sub-atomic resolution of 0.92 Å. The crystal belongs to the primitive P1 space group with unit cell parameters of a = 27.2, b = 33.7, c = 33.8 (Å), α = 97.7, β = 109.5, and γ = 104.6 (°). The Matthews coefficient of this crystal is calculated to be 1.75 ų/Da and the corresponding solvent content is 29.6%, assuming that one CssS-ECD is in the crystallographic asymmetric unit.