The microstructure and humidity‐sensitive characteristics ofα‐Fe2O3porous ceramic were investigated. Microporousα‐Fe2O3powders were obtained by controlling the topotactic decomposition reaction ofα‐FeOOH. Water vapor adsorption thermogravimetrical experiments were carried out in the relative humidity (rh) range 0% to 95% on theα‐Fe2O3powder and the 900°C sintered compact. The microstructure was investigated by SEM, TEM, Hg intrusion, and N2adsorption porosimetry techniques. The humidity sensitivity was investigated by the impedance measurements technique in 0% to 95% rh on the compacts sintered at 50°C steps in the 850° to 1100°C range. Humidity response was found to be affected by the microstructure, i.e., the characteristics of the precursor powders and sinte