ABSTRACT. The chemical composition of the essential oils obtained by hydrodistillation from Cupressus arizonica Greene, Juniperus communis L. and Mentha longifolia L. were determined by gas chromatography-mass spectrometry (GC/MS) analysis. The chemical composition of the essential oils were identified by GC/MS. Eicosane (27.4%), umbellulone (13%) and α-pinene (10.51%) were the major components of C. arizonica oil; sabinene (32%), limonene (26%) and bornyl acetate (7.4%) were the major components of J. communis oil and pulegone (26%), L-menthone (13.4%) and cis-para-menthan-3,8-diol (10.2%) were the major components of M. longifolia oil. The percentage of monoterpenes in the three essential oils was compared. The percentage of monoterpenes in C.arizonica is about 5.2%, J. communis 46%, and M. longifolia is 50.1%. The percentage of terpenes in C. Arizonica (16.3%), J. communis (5.2%) and M. longifolia (9.3%) were reported. But the percentage of cyclic monoterpenes in C. arizonica is about 6%, J. communis 26.1%, and M. longifolia is 3%. Monoterpenes are the most components that make up essential oils. KEY WORDS: Cupressus arizonica, Juniperus communis, Mentha longifolia, Essential oil, Chemical composition Bull. Chem. Soc. Ethiop. 2019, 33(3), 389-400.DOI: https://dx.doi.org/10.4314/bcse.v33i3.