New La1-xSr1+xInO4-d compounds were synthesized and identified by the powder X-ray diffraction (XRD) method. In the composition range of 0less than or equal toxless than or equal to0.2, La1-xSr1+xInO4-d compounds were prepared by heating at 1573 K in air for 36 h as single phase. Rietveld analysis of their XRD data revealed that La1-xSr1+xInO4-d compounds possess the orthorhombic K2NiF4-type structure. Measurement of electrical conductivity as a function of oxygen partial pressure (Po-2) showed oxide ion conduction for the samples below Po-2= 10(-12) atm for x=0 and below 10(-5) atm for x=0.1 and 0.2. At high oxygen partial pressure, it also showed contribution of hole conduction for the samples.