We report herein HMF (5-hydroxymethylfurfural) and furfural oxidation to 2,5-furandicarboxylic (FDCA) and furoic acids, respectively, in water, under base-free conditions and using supported gold nanoparticles. Prepared catalysts showed high catalytic activity under environmentally friendly conditions. Especially, the use of base-free conditions enables getting rid of the most usually needed neutralization step generating salts that must be further handled/eliminated. We showed that the conversion and the selectivity to desired products depend on the basicity of the support. To this respect, the Au/MgO catalyst was the most active sample (100% and 90% yields to furoic acid and 2,5-furandicarboxylic acid, respectively), although a partial leaching of Mg was observed (89 ppm). Novel Au/MgF₂-MgO catalysts were also very active (97% yield of furoic acid) with a final pH of 7.5. High yields of acid were also obtained (78%) with an acid final pH of 3.8, actually enabling the isolation of products under their acid form directly from the reaction medium without a neutralization step.