Deterioration products and processes of sweet orange oil(Citrus sinensisL. Osbeck) were investigated on the basis of simulated aging conditions. For these experiments, we employed an aqueous acidic orange oil emulsion which was exposed to UV-light at room temperature for specified periods of time. Subsequent GC/MS analysis revealed some relevant changes in the composition of the orange oil. The treatment caused a significant increase in several known compounds, such as carvone, isopulegol, isomers of carveol, the limonene and linalool oxides. On the other hand, other constituents, such as neral, geranial and citronellal, decreased. Moreover, we were also able to identify a number of newly formed secondary constituents. Among these were p-mentha-l,8-dien-4-ol, α-cyclocitral, photocitral A, iso(iso)pulegol, carvonecamphor, menthone, isomenthone, isomers of p-mentha-l(7), 8-dien-2-ol and isopiperitenol.