(Al, Ni) co-doped ZnO nanostructures were synthesized by a simple ball-milling method. The samples prepared were extensively characterized using standard techniques. X-ray diffraction analysis confirmed the coexistence of Al and Ni in the ZnO sites. The pollutant photodegradation performances of the materials were assessed by studying the removal of methyl orange and Congo red under visible-light illumination. Of the photocatalysts prepared, 2%Al-2%Ni-ZnO was found to be the most active for pollutant degradation, effecting 100% removal of MO within 30 min under visible-light illumination. This excellent catalytic activity was attributed to the strong absorption of visible light and effective separation of photoinduced charge carriers. In addition, radical-scavenging experiments were conducted to identify the key reactive species formed in the reaction, allowing a mechanistic rationale for the superior photocatalytic activity of 2%Al-2%Ni-ZnO to be proposed.