Provided is a process for the preparation of an N-substituted isothiazolinone derivative having the general formula (I), comprising reacting N-substituted 3-mercaptopropionamides of formula (II) or N,N′-bis-substituted 3,3′-dithiodipropionamides of formula (III) with sulfuryl chloride in the absence of solvents. Also provided is a process for the preparation of a compound having the general formula (III), comprising reacting a methyl ester of formula (IV) with an amine of formula (V) in a solvent of methanol. As no addition solvent is used in the process of the invention, the cost of manufacturing and pollution to the environment can be reduced.