Mesoporous gamma-Al2O3 with high surface area (159 m(2)/g) is prepared via a precipitation method. The as-synthesized Al2O3 exhibits optical absorption ability in the ultraviolet region and is used as the active component to be combined with g-C3N4 to form effective heterostructured photocatalysts. This heterojunction structure is confirmed by X-ray diffraction, scanning electron microscopy, element map, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy measurements. The photocatalytic performances of the composites are evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO). Among the prepared photocatalysts, 2g-C3N4:1Al(2)O(3) (weight ratio) exhibits the highest photocatalytic activity, the reaction rate constant of which is 2.5 and 3.7 times that of pure g-C3N4 in degradation of RhB and MO, respectively. The enhancement in activity of heterojunctions is ascribed to their high specific surface areas, excellent adsorption abilities for dyes, and efficient transfer of photogenerated electrons from the lowest unoccupied molecular orbital of g-C3N4 to the defect sites of gamma-Al2O3.