Aluminum sec-butoxide (Asb) was modified with ethyl acetoacetate (Eaa) in various ratios (Eaa : Asb = 0,5; 1; 1,5; 2; 2,5 and 3) in order to control its hydrolysis. Sols, gels and transition alumina obtained by gel thermal treatment were investigated with respect to Eaa/Asb ratio. 1H, 13C, 27Al nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), particle size analysis (PSA), scanning electron microscopy (SEM), simulataneous differential thermal and thermogravimetric (DTA/TGA) analysis and N2 adsorption/desorption isotherms were used. Five different chelates have been detected in sols: mono-chelated trimer, Al3(OsBu)8(Eaa), assymetric bis-chelated dimer, Al2(OsBu)4(Eaa)2, tris-chelated dimer, Al2(OsBu)3(Eaa)3, tetra-chelated dimer, Al2(OsBu)2(Eaa)4 and tris-chelated monomer, Al(Eaa)3. The deconvolution of 1H NMR spectra confirmed the presence of these chelates. The coordination of aluminium increases with the increase of molar ratio Eaa/Asb, thus in samples with Eaa/Asb ratio 2,5 and 3 only hexacoordinated aluminium, i.e. tris-chelated monomer, exists. This octahedral Al complex occurs as two stereoisomers, facial (fac) and meridional (mer) in ratio 2 : 3. Tris-chelated monomer is resistant to hydrolisis and it is the only chelate whose presence has been detected in hydrolized samples. Its amount in hydrolized samples is proportional to initial Eaa/Asb ratio and it is almost non-existant in sample with Eaa/Asb = 0.5 while practically whole sample with Eaa/Asb = 3 is Al(Eaa)3. Beside coordination 6 due to Al(Eaa)3, two less defined Al surroundings are noted in hydrolized samples. Two distinct morphologies can be observed in those samples, greater gel chunks and finer agglomerated chelate particles. Crystal structure of Al(Eaa)3 has been determined using powder X-ray diffraction. It crystalizes in monoclinic space group P21/n, with lattice parameters a = 16,387(1) Å, b = 19,650(1) Å, c = 6,912(1) Å and β = 91,91(1) °. The molecular structure comprises of three O,O-bidentatly linked ethylacetoacetate ligands forming octahedral coordination around the aluminium atom. Molecules are connected into chains along the b-axis by two intermolecular hydrogen bonds. Thermal treatment of gel at 800 °C for 2 hours yields pure, nanocrystalline γ-Al2O3 potentially useful as catalyst carrier. Morphology of γ-Al2O3 is also dependent on initial Eaa/Asb ratio, thus particles obtained with lower Eaa/Asb ratio are more compact while particles with greater Eaa/Asb ratio appears agglomerated. Texture is also influenced with Eaa/Asb ratio. Thermal treatment at higher temperatures results with transformation of γ-Al2O3 to α-Al2O3. Sample with Eaa/Asb ratio of 0,5 could be rated as most appropriate for catalyst carrier preparation. Investigation showed that various properties of γ-Al2O3 obtained by sol-gel synthesis can be controlled with chellating agent.