This study examined phototransformation of gamma-hexachlorocyclohexane (gamma-HCH) in different solutions. The presence of dissolved organic matter (DOM) inhibited the phototransformation of gamma-HCH. This phenomenon could be correlated to the binding interaction between gamma-HCH and DOM. alpha-Fe2O3 promoted the transformation of gamma-HCH. The humate-coated alpha-Fe2O3 revealed a slight, however significant, favorable effect compared to the bare one. Fourier transform infrared spectroscopy (FTIR) offered the direct evidence that humate-coated alpha-Fe2O3 could form surface Fe(III)-carboxylate complexes by ligand exchange. Additional experiments demonstrated that the photocorrosion of alpha-Fe2O3 coated by DOM was much more acute than that of the bare one. These combined results suggested that the transformation of gamma-HCH on humate-coated alpha-Fe2O3 is more related to a surface complex and not to a semiconductor-assisted photoreaction. In the humate-coated alpha-Fe2O3, absorption of a photon results in an excited ligand-to-metal charge-transfer state of the complexes, and a rich variety of free radical reactions ensue, which is concurrently accompanied by the dissolution of the iron oxide. Such reactions may generate reactive transients such as superoxide and hydroxyl radicals, which may be expected to transform gamma-HCH.