Abstract1‐Chlorocyclopropyl methyl ether and the corresponding sulfide are methanolysed without any rupture of the three‐membered ring. The solvolysis of 1‐halocyclopropyl sulfides has been studied kinetically and takes placeviaanSN1 mechanism. Methyl substituents in the cyclopropyl ring promote ring opening. This, and the effect of variation of the leaving group (Cl, Br, SMe2⊕), can be rationalised in terms of relative stabilities of intermediary substituted cyclopropyl and alkyl