Reducible behaviours of La_1-xSr_xFeO_3-δ(0≤x≤1.0)perovskite oxides in CO or H₂ atmosphere were studied by means of thermogravimetry (TG), differential scanning calorimetry (DSC), pulse reaction method, infrared spectrometer (IR), X-ray diffractometer (XRD) and X-ray microanalyser (EPMA). Interactions with CO or H₂ and oxygen on surface gave a large weight loss which increases with increasing x in all ranges of x in the temperature range of 525-725K.<br>Reaction with CO and reduced surface formed carbon and/or carbonaceous species with the increase in weight which is strongly dependent on gas phase CO pressure in the temperature range of 775-1125K. These reactions proceeded exothermally. It was concluded that the disproportionation reaction of CO and the formation of SrCO₃ occur more easily at both higher x values and CO pressure in the course of decomposition of La_1-xSr_xFeO_3-δ.