This study reports the deactivation mechanisms of the solid acid catalyst Amberlyst 70 during the esterification of bio-oils from mallee biomass and the methods for catalyst regeneration. The metal ions in bio-oil deactivated Amberlyst 70 via ion exchange with the hydrogen ions on/in catalyst, which changed structure of catalysts and reduced availability of acidic sites. N-containing organics reacted with the hydrogen ions on/in catalyst, forming neutral salts and resulting in complete catalyst deactivation. Polymers formed during the esterification of bio-oils deposited on/in catalyst, reducing the accessibility of catalytic sites. Washing with solvents could remove some adsorbed organics and restore some catalytic activity but not much. In comparison, ion exchange in a concentrated sulfuric acid removes most of metal ions and the N-containing organics and significantly improves the catalytic activity. (C) 2013 Elsevier Ltd. All rights reserved.