Effect of cyclodextrins (CDs) on the photodegradation of 4,4'-biphenol (BIP) in TiO2 suspension was examined using a 250W metal halide lamp (lambda >= 365 nm) as irradiation light source. The adsorption of BIP on TiO2 surface was also investigated in both conditions that CDs is absence or presence, as well as the inclusion complex of CDs with BIP. Results showed that, the behaviors of inclusion complex of BIP with CDs were the predominant factor in the photocatalytic reaction. A larger inclusion constant value (5600 M-1) of BIP with beta-CD followed by the enhancement of adsorption on TiO2 surface leads to acceleration of photodegradation, while alpha-CD showed opposite effect on the photodegradation because of a much smaller inclusion constant (51 and 355 M-(1) was obtained for alpha-CD/BIP and alpha-CD2/BIP, respectively). The reaction constants were 1.35,1.17 and 2.48 mu M min(-1) for BIP in the absence of CDs, in the presence of alpha-CD and in the presence of beta-CD, respectively. XRD analysis demonstrated that TiO2 conserved their anatase crystal features after 5-h irradiation. A trinity interaction model of BIP photodegradation in TiO2 suspension containing cyclodextrins was also proposed in this work. It would be beneficial to have a depth-in mechanism of CDs effect on reactant's photodegradation in TiO2 suspension that would probably lead to a high efficiency and selectivity for the photodegradation of pollutants using TiO2 as catalyst. (C) 2008 Elsevier B.V. All rights reserved.