According to the present invention, provided are (1) a process for the preparation of 2-chloro-5-chloromethyl-1,3-thiazole, by reacting 3- chloro-1-isothiocyanato-1-propene with a chlorinating agent, (2) a process for the preparation of 3-chloro-1-isocyanato-1-propene, by rearranging 3-chloro-1-thiocyanato-2-propene in the presence of a salt of one or more than one metal selected from the group consisting of metals belonging to Group 2A, Group 7A, Group 8 and Group 1B of the long-form periodic table, and (3) a process for the preparation of 3-chloro-1-thiocyanato-2-propene, by reacting 1,3-dichloropropene and a thiocyanate salt (a) in the presence of water, (b) in the presence of an organic solvent which is water-soluble and has a boiling point of 150° C. or lower, or (c) in an organic solvent in the presence of a phase transfer catalyst.