The production of chemicals from lignin and lignin depolymerisation products is a promising alternative route to replace fossil fuels. Transetherification of guaiacol, a lignin derived model compound, to o-ethoxyphenol with γ-Al2O3 as the catalyst in supercritical ethanol has been investigated. The best reaction condition is 280 °C for 3 h, giving a yield of 42% with a selectivity of 86%. A reaction pathway is also proposed. Besides, this work provides an example for producing a longer chain ether from a short chain ether.