The photocatalytic degradation of pahenanthrene (PHE), pyrene (PYRE) and henzo[a]pyrene (BaP) on soil surfaces in the presence of TiO2 using ultraviolet (UV) light source was investigated in a photo chamber, in which the temperature was maintained 30 degrees C. The effects of various factors, namely TiO2, soil pH, humic acid, and UV wavelength, on the degradation performance of polycyclic aromatic hydrocarbons (PAHs) were studied. The results show that photocatalytic degradation of PAHs follows the pseudo-first-order kinetics. Catalyst TiO2 accelarated the photodegradation of PHE, PYRE and BaP significantly, with their half-lives being reduced from 533.15 to 130.77h. 630.09 to 192.53h and 363.22 to 103.26h respectively, when the TiO2 content was 0.5%. In acidic or alkaline conditons, the photocatalytic degradation rates of the PAHs were greater than those in neutral conditions. Humic acid significantly enhanced the PAH photocatalytic degradatio by sensitizing radicals capable of oxidizingg PAHs. Photocatalytic degradation rates of PYRE and BaP on soil surfaces with 2% TiO2 were different at UV irradiation wavelengths of 254, 310 and 365 nm, respectively. The synergistic effect of UV irradiation and TiO2 catalysis was efficient for degradation of PAHs in contaminanted soil. (C) 2008 Elsevier B.V. All rights reserved.