The effect of harvesting period on the oil production was examined on fiveEucalyptusspecies(E. camaldulensis, E. globulus, E. globulus ssp. maïdenii, E. melliodoraandE. bosistoana)of Moroccan origin. For some species such asE. camaldulensis, E. globulus and E. globulus ssp. maïdenii, the oil yield seemed to depend on the harvesting season. The period ranging from June to October gave the best yield with a maximum in June. The 1,8-cineole contentof Eucalyptusoil may also vary during the year. This was observed in the case ofE. globulusandE. melliodora, although the observed changes were rather random. The month for maximum 1,8-cineole content varied depending upon the species.