The essential oil, which was obtained by steam distillation from two qualities of mastic gum, was subjected to analysis by GC and GC/MS. It was found that the oil contained 62 constituents, 61 of which were identified. The main components were α-pinene (58.86–77.10%), camphene (0.75–1.04%), β-pinene (1.26–2.46%), myrcene (0.23–12.27%), linalool (0.45–3.71%), and β-caryophyllene (0.70–1.47%). These six components total more than 90% of the oil. Some qualitative and quantitative differences were found between the two oils.