The photolysis of chlorohydroquinone (QH 2 Cl) in aerated or degassed solution leads to the formation of hydroquinone (QH 2 ) and chlorobenzoquinone (QCl) as the main photoproducts. In the initial stage of the reaction, they are formed at the same rate and account for about 80% of QH 2 Cl converted. The formation of benzoquinone (Q) and chlorohydroxybenzoquinone (QOHCl) was also observed and evaluated. The conversion into Q is favoured by dilution. QOHCl results from a secondary reaction. A radical mechanism involving semiquinone and chlorosemiquinone radicals is proposed, since transients absorbing in the range 400-450 nm were detected by flash photolysis. The UV spectrum of QCl . - can be observed without irradiation in a basic solution of QH 2 Cl. It is red shifted by about 7 nm compared with the spectrum of Q . - . The formation of QH 2 , previously observed in the induced photo-oxidation of 2-chlorophenol and 3-chlorophenol, is attributed to the photolysis of QH 2 Cl formed in the initial stage of the reaction.