The stability of Novozym Ò 435 in the esterification of ibuprofen using ethanol as reactant and solvent was investigated. Additionally, the surface interaction of the isomers of ibuprofen and ethanol with the biocatalyst was screened through conventional adsorption isotherms and temperature programmed surface reaction (TPSR). These investigations evidenced strong alcohol adsorption and dissolution of the biocatalyst, which explains its deactivation upon reuses in the esterification reaction.