Precursor powders with antimony-to-iron (Sb/Fe) atomic ratios ranging from 0 to 2.0 were prepared by chemical coprecipitation. The origin of enhanced gas-sensing behavior at a higher calcining temperature was investigated, based on phase evolution and microstructure characterized by means of thermal analysis, x-ray diffraction, Brunauer–Emmett–Teller surface area measurement, and electron microscopy. Only one iron–antimony oxide (i.e., FeSbO4) could be obtained under present experimental conditions. Pure FeSbO4 exhibited a high gas sensitivity, only when calcining temperature was below 600 °C. A rapid crystallite growth, as well as hard agglomeration, occurred in pure FeSbO4 powder calcined at 600–1000 °C, and thus led to poor gas-sensing behavior. However, there existed an optimal Sb/Fe ratio range (i.e., 0.25 to 0.65) in which crystallite growth of both α–Fe2O3 and FeSbO4 could be efficiently depressed up to 800 °C. The samples (with Sb/Fe ratio in the range 0.25–0.65) calcined at 600–800 °C displayed a high sensitivity to liquid petroleum gas due to their large specific surface area and poor crystallinity.