Perovskites of the system Pr_1-xSr_xMn_1-yIn_yO_3-δ have been investigated in terms of their applicability in high temperature electrochemical devices. Thereby the stability, thermal expansion and conductivity properties in different oxygen partial pressures have been examined. Pr_0.5Sr_0.5MnO_3-δ shows a p-type conductivity of 135 S/cm at 700 °C and in a partial pressure range from p(O₂) = 20 kPa (air) to p(O₂) = 2·10^-3 kPa (argon) which slightly decreases to 105 S/cm at p(O₂) = 10^-14 kPa. The coefficient of thermal expansion does not vary between air and argon and is close to values of state of the art electrolytes. Therefore Pr_0.5Sr_0.5MnO_3-δ is a promising candidate for the application as the cathode material in a solid oxide fuel cell. Partial substitution of praseodymium by strontium increases the amount of oxygen vacancies and therefore increases the ionic conductivity when no multivalent B-site cation is involved. A solubility limit of x = 0.2...0.3 exists for Pr_1-xSr_xMn_1-yIn_yO_3-δ (y = 0.5; 1) perovskites. Exceeding this limit leads to the formation of a secondary phase which is identified as SrIn₂O₄. The ionic conductivity of Pr_0.5Sr_0.5InO_3-δ reaches 3·10^-3 S/cm from air to p(O₂) = 4·10^-16 kPa at 700 °C. Due to the incorporation of the insulating secondary phase SrIn₂O₄ the real ionic conductivity of the phase pure perovskite is expected to be higher. Therefore this material is promising for the application in high temperature electrochemical devices when oxygen ionic conductivity is required.