The high quality ylang-ylang essential oil has been used as an irreplaceable cosmetic product of world-wide fame. The degree of commercial differentiation of the oil is based basically on the content of oxygenated compounds. The oil was obtained by distillation of the flowers of the tree of Cananga odorata. A relation between the time of the year and the chemical composition of the oil was determined. The flowers were collected monthly during the years 2005 and 2006. The monoterpene hydrocarbons and their oxygenated analogs presented a greater content during March and May. The oxygenated sesquiterpenes presented a high percentage in April and October. The greater yield of the essential oil was observed in the months of May, June and July (0,5%). The smaller percentage appeared in October (0,3%).