To provide a method for producing 5-{4-[2-(5-ethyl-2-pyridyl)ethoxy]benzyl}-2-imino-4-thiazolidinone in high efficiency and in high purity.

Provided is a method for producing 5-{4-[2-(5-ethyl-2-pyridyl)ethoxy]benzyl}-2-imino-4-thiazolidinone highly slight in dimerized impurities, which comprises a process wherein 4-[2-(5-ethyl-2-pyridyl)ethoxy]aniline is reacted with a nitrite in the presence of hydrochloric acid, followed by the reaction with methyl acrylate in the presence of a copper catalyst, to obtain methyl 2-chloro-3-{4-[2-(5-ethyl-2-pyridyl)ethoxy]phenyl}propionate, and the resultant product is then reacted with thiourea in the presence of an alkali.