Compounds of nominal composition, In2-xMnxO3-delta (0.001 <= x <= 0.25) were investigated for their hydrogen sensing characteristics. Three compositions, namely, In1.99Mn0.01O3-delta, In1.985Mn0.015O3-delta, In1.98Mn0.02O3-delta were found to sense 100 10 20000 vppm of hydrogen at 623 K and In1.985Mn0.015O3-delta was the most promising among them. A systematic decrease in electrical conductivity with the increase in manganese concentration was observed. Mechanism of hydrogen sensing of In1.985Mn0.015O3-delta probed by core shell X-ray photoelectron spectroscopy and valence spectra revealed the presence of In+ ion. (C) 2015 The Electrochemical Society. All rights reserved.