Nowadays, macroalgae are widely discussed as advantageous alternative feedstock for crude bio-oil production using pyrolysis. In the present work, pyrolysis products of Enteromorpha clathrata washed with 7% phosphoric acid, hydrochloric acid and sulfuric acid were studied. In general, washing with diluted acids resulted in significant increase in the yields of bio-oil and non-condensable gas over the control in favor of the bio-char. In addition, HCl pretreatment enhanced the relative contents of aliphatic hydrocarbons in the bio-oil by 1.5 times over the control. Furthermore, HCl pretreatment showed 37% and 52.6% reduction in acids and oxygen-containing compounds, respectively, with respect to the control. FTIR analysis showed that acid-washing led to reduction in O-H stretching vibration, confirming that it can disrupt hydroxyl bonds reducing phenols, carboxylic acids and water impurities in the bio-oil. In conclusion, washing of biomass using diluted acids could play a key role to enhance the bio-oil yield and significantly influence products characteristics; particularly, HCl enhanced bio-oil yield with higher aliphatic hydrocarbons proportion. (C) 2019 Elsevier Ltd. All rights reserved.