Chloromethyl methyl sulfide is the organosulfur compound with the formula ClCH2SCH3.

In terms of functional groups, it is a thioether and an alkyl chloride.

The compound is structurally related to sulfur mustards, i.e., it is a potentially hazardous alkylating agent.

The compound finds some use in organic chemistry as a protecting group.

In the presence of base, it converts carboxylic acids (RCO2H) to esters RCO2CH2SCH3.