The role of acceptor and donor defects in epitaxial Al-doped SnO2 films were systematically investigated. Al doping introduces acceptor defects (Al-Sn) at low doping concentration while donor ones (Al-i) in a concentration range from 8 to 10 at%. The band gap is firstly narrowed by hole-doping and then widened by electrons introduced by oxygen vacancies and Al-i. Air-annealing absorbs oxygen and makes Al ions transformed from Al-Sn to Al-i, corresponding to a decrease (increase) in the band gap when most Al ions occupy the substitutional (interstitial) sites. The saturation magnetization of the films is enhanced by Al-Sn doping, with the maximum value in the Sn0.98Al0.02O2 film. The magnetic moment is contributed by the localized holes introduced by Al-Sn. The existence of the ferromagnetism induced by holes in the film with oxygen vacancy gives a new insight into the behavior of defects in SnO2. (C) 2015 Elsevier B.V. All rights reserved.