PURPOSE: To prepare the titled compound economically in an industrial scale in high yield, by reacting bromochloromethane with a thiocyanic acid salt in the presence of water using polyethylene glycol and/or its alkyl ether, etc. as a catalyst.

CONSTITUTION: Chloromethyl thiocyanate is prepared by reacting bromochloromethane with a thiocyanic acid salt in the presence of water. The reaction is carried out using polyethylene glycol, polyethylene glycol monoalkyl ether, polyethylene glycol dialkyl ether or polypropylene glycol as a catalyst. The average molecular weight of the catalyst is 200W20,000, preferably 600W6,000. The rate of reaction can be remarkably improved by the use of the catalyst, and a high yield can be achieved even by the reaction under normal pressure. The amount of the catalyst is 0.1W10wt%, preferably 0.5W5wt%, based on the thiocyanic acid salt.