[en] This paper reports the synthesis, morphology, magnetic properties and gas sensing characteristics of mesoporous urchin-like α-Fe_2O_3 superstructures prepared by one-step thermal decomposition of iron nitrate aqueous solution. The advantages of this fabrication technique include simplicity, convenience, efficiency, capability of scale-up fabrication, and good control of product structure and morphology. The urchin-like α-Fe_2O_3 superstructures are made of oriented aggregations of nanorods (diameter ∼ 10–130 nm; length ∼ 150–700 nm) with an overall size in the range of 0.5–5 μm. The nanobuilding blocks of the urchin-like superstructures are either single-crystal nanorods or a mixture of single-crystal knotted or branched sub-nanorods and elongated particles. Unusually high intrinsic coercivity, _iH_c, of up to 5.3 kOe and reduced Morin transition temperatures were observed for the urchin-like α-Fe_2O_3 superstructures. The urchin-like α-Fe_2O_3 samples showed excellent gas sensing performance for acetone, ammonia, and ethanol. (paper)