Cobalt (Co) doped AZO (2 at.% Al doped ZnO) thin films were synthesized by sol-gel technique. The films were found to have polycrystalline wurtzite structure of ZnO. The structural, morphological and transport properties of the films were investigated and found to be strongly composition dependent. Grain size and room temperature resistivity of the films were found to decrease with increase of Co content in the AZO films from 1 to 3 at.%. Beyond 3 at.% these parameters were found increasing. The electrical resistivity of the films was measured down to temperature of 100 K. The carrier transport mechanisms have been explained on the basis of thermionic emission and variable range hopping. © 2009 Elsevier B.V. All rights reserved.