Abstract: In the technology for producing 1,2-dichloroethane by reacting ethylene with chlorine by a liquid phase reaction at 65.degree. to 160.degree. C. in 1,2-dichloroethane containing a metal chloride catalyst, there is a disadvantage of a side reaction for producing 1,1,2-trichloroethane etc. at a large ratio to cause lower yield of 1,2-dichloroethane. The present invention is to overcome the disadvantage and to produce 1,2-dichloroethane in high yield by reducing the side reaction by incorporating at least one of aromatic compounds selected from the group consisting of benzene type hydrocarbons having the formula ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 respectively represent hydrogen atom, C.sub.1 -C.sub.5 alkyl group and chlorinated derivatives thereof as a side reaction inhibitor at a ratio of at least 0.001 wt. % in the reaction medium.