Mg/Cd doped Mn:ZnO thin films have been prepared by a sol-gel method. Our results indicate that Mg and Cd-doping can tune the bandgap of ZnO film (3.17-3.30 eV), and all of these thin films show room temperature ferromagnetic behaviors. As the bandgap of ZnO-based thin films changes, it effects the strength of the magnetic exchange interaction in the transition metal doped ZnO films, which results in the tunable ferromagnetism. This may be a practical way to achieve appropriate dilute magnetic semiconductor materials for future spintronic devices. (C) 2013 Elsevier B.V. All rights reserved.