Chemical looping of bio-oil is a promising route to convert this low-quality fuel to pure hydrogen with inherent gas separation and low energy penalty. In that the oil is liable to form coke during the heating process, the current chemical looping cycles usually suffer from low hydrogen purity and poor OC recyclability. In this paper, we proposed a strategy of adding steam in FR to suppress coke formation and enhance the hydrogen purity. To perform the chemical looping cycles, we first built a dual fluidized bed and attained the optimal operating conditions. The results showed the higher hydrogen purity, yield and good recyclability at 950 degrees C. Afterward, we investigated effects of the steam to oil ratios on hydrogen purity, yield and the recyclability of oxygen carrier, and found adding steam in the fuel reactor was an efficiency way to enhance the hydrogen purity. The results suggested the hydrogen purity can reach 98%; nevertheless, it suppressed the hydrogen yield simultaneously. In terms of the redox performance of oxygen carrier, we also found the steam can weaken the reduction reactions, and therefore increased the particle recyclability. Our current study suggested the enhancement of the hydrogen purity was at the cost of the suppression in hydrogen yield, and we need to find a compromise between the hydrogen yield and the purity to pursue high system efficiency. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.