The oleuropein hydrolytic conversion, under biomimetic conditions, induced by the endogenous enzymatic system of the olive fruit, has been monitored by the intermediate derivative formation through (1)H and (13)C NMR spectra; the assigned molecular structures reveal the identity of new bioactive biophenolic metabolites, the hemiacetal aglycon, and the two epimeric dialdehydes, which influence the pathogen antagonism of olive fruits and the hedonistic-sensorial characteristics of olive oil.