The catalytic effect of boric oxide on the pyrolysis of empty palm oil fruit bunch (EFB) and oil palm fronds (OFF) in a fixed-bed reactor at 400 degrees C was investigated. Boric oxide was found to selectively reduce 50-80% of the hydroxyl and methoxy groups in both water soluble (WS) and non water soluble (NWS) fractions of the oil. The increase in water and char yield suggested that pyro-catalysis of boric oxide enhanced the cleavage of C-O bonds in the biomass polymers and the capability to retain the inherent oxygen of the biomass in the solid product. This allows organic compounds with less oxygen substitution to become volatile and condenses as bio-oil. A mechanism for pyrolysis of boric oxide with biomass showing the hydroxyl removal pathway is proposed in this study. (C) 2011 Elsevier B.V. All rights reserved.