Abstract: Spinel-type complex oxide nanocrystalline powders CdFe₂0₄ was synthesized by solid-statereaction and decomposition at low temperature with inorganic reagent. The results of XRD and TEM indicate that the solid-state reaction is complete and the mean grain size of the powder is about 30nm. Compared with the traditional methods, the solid state reaction at low temperature decreases the forming temperature of spinel phase. The gas-sensing properties of the pure powders were studied. The results reveal that the sensors based on CdFe₂0₄ show a high sensitivity and selectivity to H₂S at low working temperature.