Background: The genus Eucalyptus (family Myrtaceae) comprises well-known plants of over 600 species of trees. Although most of the plants are native to Australia, numerous species have been introduced to other parts of the world, including Iran, as economic and ornamental trees in forest trial provenances, where the plants have become source of important fast-growing hardwood trees and Eucalyptus oils.Objective: Aim of this studu is to determine chemical composition in essential oils of Eucalyptus for medicinal uses.Methods: The essential oils isolated by hydrodistillation from the leaves of two Eucalyptus viridis R. Baker and Eucalyptus oleosa F. Muell. were analysed by GC and GC/MS.Results: The main components identified in E. viridis oil were 1,8-cineole (84.7%), a - pinene (4.4%), trans-pinocarveol (2.2%) and in E. oleosa were 1,8-cineole (89.4%), b- pinene (1.2%) and a - pinene (1%).Conclusion: The chemical composition of the oils with high content of 1,8-cineole (84.7 and 89.4%) are classified as a "eucalyptol or medicinal" type.