Chemical looping hydrogen generation by the iron-based oxygen carrier redox cycle is promising thanks to its inherent CO2 separation and low energy penalty. Bio-oil heavy fraction, characterized as the oil fraction of pyrolysis bio-oil and difficult to be upgraded for bio-fuel or chemicals production, was used as the feedstock to generate hydrogen for the hydrodeoxygenation process of aqueous phase of pyrolysis bio-oil. The result showed the successful-generation of hydrogen by this process, but the undesired carbon formation on the iron-based oxygen carrier resulted in the low purity hydrogen. To avoid this, removal of deposited carbon by the introduction of steam vapor in the fuel reactor was proposed and evaluated. The result confirmed that the positive role of steam vapor played on the enhancement of hydrogen purity, over 99% of hydrogen concentration was obtained in the case of steam to oil ratio at 2.0. However, the hydrogen purity and hydrogen production were in a competing relationship and the hydrogen purity enhancement inevitably suppressed the hydrogen production after steam vapor addition. By taking account of the hydrodeoxygenation process of aqueous phase of pyrolysis bio-oil, the steam to oil ratio of 1.2 was preferred. (C) 2015 Published by Elsevier B.V.