gamma-Fe2O3 nanoparticles with magnetic properties can be obtained by thermal decomposition in air of iron nitrate-polyethylene glycol (PEG) mixtures. In this paper we report a study regarding the obtaining of the single phase, well crystallized gamma-Fe2O3 spinel, that takes place directly by thermal decomposition at similar to 300 degrees C without other thermal treatments. PEG acts as a reducing and coating agent of iron oxide and limits the agglomeration of gamma-Fe2O3 nanoparticles. We studied the obtaining of gamma-Fe2O3 by thermal decomposition of PEG-iron nitrate mixtures by thermal analysis and Fourier transform infrared spectroscopy. From the thermal behavior of the samples prepared using different PEG-iron nitrate ratios, we have established 300 degrees C as annealing temperature. The obtained powders were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and magnetic measurements. It was established that the obtaining of gamma-Fe2O3 at 300 degrees C as single phase requires a minimum PEG-iron nitrate molar ratio of 0.25:100. The resulting gamma-Fe2O3 particles had a spherical shape and an average size smaller than 10 nm, in agreement with the average crystallite size calculated from XRD patterns. The obtained gamma-Fe2O3 powders presented magnetic properties, which are influenced by the molar ratio of the reactants. (C) 2015 Elsevier B.V. All rights reserved.