CoFe2O4 thin films of different thicknesses were grown on SrTiO3 substrates. The X-ray diffraction analysis and atomic force microscopy indicated both epitaxy and a granular microstructure. We studied the magnetic properties of these films as a function of oxygen post-annealing and film thickness. All as-deposited films exhibited similar magnetic properties with saturated magnetization (M-s) of approximately 50% of the bulk M-s, (80 Am-2 kg(-1)). After the post-annealing the M-s changes as a consequence of crystallographic restructuring of the film. Cation ordering in 100 nm thick films reduces M-s, whereas re-oxidation increases M-s for thinner films. 13 nm films, annealed for 1 h, reach the bulk M-s. For even thinner films the quantum-size effect reduces M-s. For a synthesis of >= 30 nm films an annealing cycle after deposition of every 15 nm layer is recommended. (C) 2009 Elsevier B.V. All rights reserved.