Polypyrrole (PPy)/gamma-Fe2O3 hybrid materials were prepared by sal-gel polymerization in situ and characterized by Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA) and high-resolution transmission electron microscope (HRTEM). The gas sensitivities in CO, H-2, NH3, ethanol or acetone atmospheres were determined at 30 degrees C, 60 degrees C and 90 degrees C. FT-IR and XRD patterns suggest that ferric oxide in the hybrids was. gamma-Fe2O3, with a diameter of approximately 5 nm. TG-DTA and HRTEM analyses showed that different reactant molar ratios of pyrrole monomer: Fe(NO3)(3)center dot 9H(2)O resulted in different microstructures of gamma-Fe2O3 and molecular weights of PPy. An increased amount of Fe(NO3)(3)center dot 9H(2)O increased the degree of uniformity of the molecular weight of PPy and resulted in a change of gamma-Fe2O3 microstructure from granular to stick particles. The results of gas sensitivities showed that the PPy/gamma-Fe2O3 hybrids exhibited high sensitivity to NH3 at mild operating temperature (<100 degrees C). Furthermore, the sensing mechanism was also discussed. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.