The chemical contents and compositions of four essential oils extracted from leaves, branches, fruits and gum-resin of Juniperus excelsa from Jabal Al-Akhdhar in the Sultanate of Oman were studied using infra-red (IR) spectroscopy and gas chromatography-mass spectrometry (GC-MS). IR analysis revealed the presence of C-H, O-H, C=C and C=O functionality bonds with varied intensities. The GC-MS study showed the occurrence of 35 different monoterpenes of which 11 (31.43%) monoterpenes were shared by the four oils. α-Pinene was detected in branches and gum-resin oils as a major compound with different proportions (80.50% in gum oil and 79.03% in branches oil). The major component in leaf and fruit oils was the monoterpene limonene with proportions of 50.46% and 42.51%, respectively. Sesquiterpenes exist in leaf, branch and fruit essential oils but not in gum-resin oil. The essential oil of the leaves showed stronger antioxidant and radical scavenging activities than the other oils.