Aluminium doped yttrium-iron garnet (YIG) nanoparticles (Y 3AlxFe5-xO12, x = 0, 1,5, 1,55, 1,575, 1,6) have been prepared by the nitrate-citrate sol-gel auto-combustion method (NCSAM). Our goal was to prepare YIG nanopowders with different aluminium content, furthermore to investigate the variation of the Curie temperature of the samples in function of the amount of dopant cations. The crystalline phase attributes, microstructure, morphology, surface area, Curie temperature (T C) and permeability of the sintered powders were characterized using X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), surface area measurement (BET) and ac magnetic permeability with frequency shift. The results show, that the sintered powders exhibit a spongy-like morphology with relatively high surface area. Furthermore it has been confirmed, that the ac magnetic permeabilities are strongly depending on the chemical composition.