We here report on the enzymatic synthesis of the antiviral drug Vidarabine (arabinosyladenine, araA) starting from arabinosyluracil and adenine. To this aim, uridine phosphorylase from Clostridium perfringens (CpUP) and a purine nucleoside phosphorylase from Aeromonas hydrophila (AhPNP) were used as covalently immobilized biocatalysts. Upon investigation of the optimal conditions for the enzyme activity (phosphate buffer 25 mM, pH 7.5, 25 ° C, DMF 12.5-30%), the synthesis of araA was scaled up (2 L) and the product was isolated in 53% yield (3.5 g/L) and 98.7% purity. A E-factor comparison between the enzymatic synthesis of araA and the classical chemical procedure clearly highlighted the “greenness” of the enzymatic route over the chemical one (E-factor: 423 vs 1356, respectively).