Abstract: Duration of distillation is one of the important factors affecting quality and yield of the essential oil of Melaleuca alternifolia.Investigations on chemical constituents and yield of M. alternifolia oils collected at different times during distillation were carried out in this paper.Results showed that the main chemical components and yield of M. alternifolia oils were decreased accompanying increased duration,while sequiterpenoids increased.The oil yield is over 98% in the duration of 0-120 min,and it is less than 2% during 120-150 min.Thus,improved oil quality and decreased energy consumption could be resulted by controlling the duration of distillation.

Key words: Melaleuca alternifolia, essential oil, terpinen-4-ol