Some of the plants used in Saudi folk medicine without or with a little data about their phytochemical constituent. The HPLC-PDA profile of phenolic constituents, essential oil composition by GC-MS and antioxidant capacity were analyzed by the DPPH assay for six Plectranthus species (P. arabicus, P. asirensis, P. pseudomarrubioides, P. barbatus, P. hijazensis and P. aegyptiacus) growing in Saudi Arabia. The essential oil content of the studied plants was varied from 0.1% to 0.3% v/w of the aerial parts fresh weight, a total number identified compounds were 110 and their compositions mainly composed of monoterpene hydrocarbons (18.79, 8.52, 39.14, 71.27, 0.97, 26.77%), oxygenated monoterpenes (33.72, 8.16, 25,51, 0.75, 4.59, 58.49%), sesquiterpene hydrocarbons (9.27, 26.06, 2.55, 0.00, 30.48, 9.11%), and oxygenated sesquiterpenes (30.23, 33.38, 24.36, 0.00, 44.20, 0.00%) respectively. Thymol was the only phenolic component detected in P. aegyptiacus with highest concentration 58.49%. The HPLC profile of these plants were recorded and it imply for close similarity with minor differences between the six species of Plectranthus and showed that the presence of gallic and rosmarinic acids in all species except P. aegyptiacus which did not contain gallic acid. All samples showed strong anti-free radical activity in comparison with trolox and ascorbic acid.