Chloroethane, a kind of genotoxic impurity, may be produced during the preparation of besifloxacin hydrochloride. Controlling the residue of chloroethane in the final product is one of the important quality indexes of besifloxacin hydrochloride. In this research, a method using DB-624 capillary column, direct injection, and programmed temperature was developed for determination of the residue of chloroethane in besifloxacin hydrochloride, and sample preparation and injection process were operated at low temperature This method is simple, sensitive, accurate and reproducible.