Although great potential hazards and threats still occur from sulfur mustard, there are no specific medicine or therapy for the intoxication of sulfur mustard. Herein, we have demonstrated a supramolecular approach for the detoxification of the sulfur mustard simulant CEES (4) in vitro and in vivo by carboxylatopillar [5]arene potassium salts (CP[5]AK 1) efficiently based on host− guest interactions. The encapsulation of CEES (4) by the cavity of the pillar[5]arene 2 is driven by C−H•••π interactions between CEES (4) and the electron-rich cavity of pillar[5]arene 2, which was investigated by 1 H NMR titration, density functional theory studies, and the independent gradient model studies. CEES (4) is degradated to the reactive sulfonium salts quickly in aqueous media, resulting in the alkylation of DNA and proteins. The sulfonium salts can be encapsulated by CP[5]AK 1 efficiently, which accelerates the degradation of the sulfonium salts about 14 times. The cell and animal experiments indicated that the bioactivities of the sulfonium salts are inhibited with the formation of stable host− guest complexes, and CP[5]AK 1 has a good therapeutic effect on the damages caused by CEES (4) at either pre-or posttreatments. Due to the low cytotoxicity and good therapeutic effect, the anionic pillar [5]arenes are expected to be developed as specific antidotes against sulfur mustard (HD).