Presented work concerns BIVOX based solid electrolytes doped with lanthanum and praseodymium. Investigations of melting point and composition of new materials were performed by use of DTA and X-ray measurements. For determination of conductivity the impedance spectroscopy (IS) method was applied. Measurements were performed in wide range of frequency 20 Hz – 1 MHz and temperature 150 – 750 oC. The electrical measurements allowed evaluation of possible application in SOFC.