Bi-2(Fe1-x Al (x) )(4)O-9 (x = 0, 0.1, 0.3, 0.5, and 0.7) samples were synthesized by a simple hydrothermal method. The samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transformed infrared spectra, N-2-sorption, and UV-Vis diffuse reflectance spectra, and their photocatalytic activities were evaluated by the degradation of methyl orange under visible-light irradiation. The results reveal that the Al substitution can effectively improve photocatalytic performance, which is attributed to the increase of surface area, the improvement of energy band structure, and the distortion of the Fe-O octahedron in Al-substituted samples. In addition, it is found that the photocatalytic activity to decompose methyl orange under visible-light illumination increases monotonically as x increases from zero to 0.5 in Bi-2(Fe1-x Al (x) )(4)O-9 and then decreases for x = 0.7, which is believed to be associated with the distribution of Fe3+ ions over the octahedral and tetrahedral sites.