Abstract In this study, enzymatic synthesis of galactoside of salicin, compound with potential physiological activity due to structural resemblance with galectin inhibitors, and analgesic and antipyretic properties of salicin, was performed using β-galactosidase from Aspergillus oryzae. It was determined, using HPLC and ion mobility mass spectrometry, that enzymatic synthesis was highly selective since only one isomer was formed via primary hydroxyl group on glucose moiety of salicin. The optimization of key experimental factors using response surface methodology enabled galactosyl salicin concentration up to 30.8 mM obtained at lactose concentration 40 mM, salicin concentration 110 mM, enzyme amount 360 IU and reaction time 12 h.