Chemical stability and high electrical conductivity under the operating conditions of solid oxide fuel cell (SOFC) are considered as the momentum for innovating solid electrolytes and electrodes. In this paper, we report synthesis, structure, chemical stability and electrical conductivity of novel co-doped Ce0.s(-5)Y01Mn(50)2,5 (x = 0-15 mol%) (CYM0). X-ray diffraction of Mn and Y-doped CeO2 shows the formation of fluorite-type structure with a space group Fm-3m. A few weak peaks corresponding to a tetragonal Mn304 phase has been detected in some samples. Solubility of Mn in ceria is explained by considering the influence of the ionic radius, the crystal structure and its electronic structure. Thermal analysis shows dissimilarity between the reduction behavior of Ceo.oMn0102,5 and Ce(0.)9(-5)Y(01)Mn5(02-)6. Ce(0)sY(05)Mn(0:1)O(2,5) exhibited the highest conductivity of -6 x 10(-2) S cm(-1) and 0.15 S cm(-1) at 700 degrees C in air and H-2, respectively. Surface studies have confirmed the formation of S species upon exposure to 30 ppm H2S in H-2 and a mechanism for S poisoning is presented. (C) 2013 Elsevier B.V. All rights reserved.