Ultra-fine γ-Fe 2 O 3 powders with average particle size of 10 nm were prepared by a complexing sol-gel process. Thermal analysis, X-ray diffraction and FT-IR were employed to study the microstructure and thermal stability. The as-prepared γ-Fe 2 O 3 has high response to reducing gases. γ-Fe 2 O 3 doped with Y 2 O 3 to form a solid solution can raise its phase transition temperature to as high as 775 o C and improve the resistance stability of the sensors without great change of their response and selectivity. The lifetime problem of gas sensors based on γ-Fe 2 O 3 is expected to be basically solved by doping method.