Graphite rods were modified by substituted aryldiazonium salts allowing subsequent laccase immobilisation and direct electron transfer at the cathode. Two covalent enzyme immobilisation methods were performed with carboxy and amino substituted grafted groups, either via the formation of an amide bond or a Schiff base between the glycosidic groups of the enzyme and the amino groups on the electrode surface, respectively. Laccase adsorption efficiency was consistently compared to the covalent attachment method on the same carbon surface, showing that the latter method led to a higher immobilization yield when the electrode surface was functionalized with carboxylic groups, as shown from both laccase activity measurement toward an organic reducing substrate, ABTS, and quantitative XPS analysis. Both analytical methods led to similar laccase surface coverage estimation. From activity measurements, when laccase was covalently immobilized on the electrode functionalized with carboxylic groups, the surface coverage was found to be 43±2% whereas it was only 10±3% when laccase was adsorbed. Biocatalyzed dioxygen reduction current was also higher in case of covalent immobilization. For the first time, oxidized laccase performances were compared to unmodified laccase, showing significant improved efficiency when using oxidized laccase: the current obtained with oxidized laccase was 141±37 μAcm- 2 compared to 28 ± 6 μAcm- 2 for unmodified laccase after covalent immobilization of the enzyme on a graphite electrode functionalized with carboxylic groups.