In this work, a computational technique based on semiempirical SCF MO method MSINDO, has been used for investigation of the adsorption and photocleavage of para-chlorophenol (p-CP) molecule on the anatase TiO 2 (001) and (100) surfaces. The surfaces have been modeled with two saturated clusters Ti 21 O 58 H 32 and Ti 36 O 90 H 36 . The optimization of the perpendicular conformation of p-CP molecule relative to the anatase TiO 2 (100) surface, has resulted in a linkage of the molecule to the surface titanium atom via phenolic oxygen atom. We studied the aromatic ring cleavage by singlet oxygen ( 1 O 2 ) and superoxide radical anion (O2•-) and accordingly, relevant mechanisms are suggested. The results reveal that the ring opening path of p-CP molecule on TiO 2 (100) surface, following the single electron transfer/O2•- mechanism, is energetically more favourable than the 1 O 2 /dioxetane mechanism.