Abstract: Although voluminous literature can be found in regard to the production of Chlorobenzene from benzene and chlorine, it is considered necessary to make some further investigations. The major variables studied in the present work are temperature, concentrations of the reactants, kinds of catalysts, and the effect of air admixed in the chlorine gas. It is known from the experimental results that the yield of chlorobenzene decreases while that of dichlorobenzene incroases with inerease in temperature. The temperature between 25?and 30℃ can be considered as most suitable for industrial production as regards the catalysts, anhydrous alumminum chloride and the residue remained after distillation of the reaction mixture are the best. Anhydrous ferric chloride is a little worse than the two just mentioned but slightly better than metallic iron. Any air mixed in the chlorine gas has only very little effect on the chemical reactions. If one desires to obtain as little dichlorobenzene as possible in comparison with the amount of chlorobenzene obtained, it is suggested to use 0.8 mol chlorine per mol of benzene when the temperature is 30℃ and iron is used as catalyst. Under these conditions, the highest ratio of the amount of chloro-benzene to that of dichlorobenzene will obtained.