We report the Al-doping contents dependence of crystal growth and energy band structure in Al:ZnO thin films on the quartz substrates by the sol-gel method. As the Al contents increase, the At-doping in the lattice reveals a maximum while the dopant is 2 mol%. It is inferred that the doping deterioration attributes to the decrease of grain size, which might be induced by the pinning effect of amorphous Al2O3 on ZnO grains boundary. The blueshifts of optical bandgap imply the quantum size effect of crystallites and the Burstein-Moss shifts in photoluminescence spectra indicate the heavy doping level for all samples. (C) 2009 Elsevier B.V. All rights reserved.