Decomposition of organic chlorine compounds was investigated in a dielectric barrier discharge photocatalystic reactor. A porous anodized aluminum plate supporting a photocatalyst of titanium (IV) oxide (anatase form) was used as a discharge electrode. The effects of space velocity, species of carrier gas and concentration of reactant gas on the decomposition of monochlorobenzene and o-dichlorobenzene were investigated experimentally. The effect of photocatalyst on the decomposition of o-dichlorobenzene was also investigated. Monochlorobenzene and o-dichlorobenzene were decomposed completely by the discharge reaction at room temperature. Addition of oxygen or steam to the carrier gas decreased the decomposition reactivity. Use of the photocatalyst on the electrode promoted the decomposition. Decomposed chlorine compounds were not converted to hydrogen chloride completely.