In this study, the total phenolic amounts and antioxidant activities of plant extracts obtained from some common Mediterranean plant species collected from different places in Jordan were determined. The phenolic constituents of these extracts were also determined using HPLC. The total phenolic amounts ranged from 52.8 to 876.9 mg GAE per 100 g dry material. The antioxidant activities were evaluated according to the 2,2-diphenyl-1-picrylhydrazyl radical scavenger method. Sage (Salvia officinalis) showed the highest antioxidant activity (91%), while the lowest (11.3%) was seen in parsley (Petroselinum crispum). A strong correlation (r  =  0.85) between antioxidant activity and total phenolic content was found. The phenolic compounds identified by HPLC were gallic acid, protocatechuic acid, catechin, gentisic acid, chlorogenic acid, vanillic acid, syringic acid, caffeic acid, epicatechin and benzoic acid. All the investigated plants contain gallic acid, whose phenolic content ranged from 0.4 to 37.8 mg per 100 g, catechin (0.3–339.9 mg per 100 g), protocatechuic acid (0.3–41.9 mg per 100 g) and gentisic acid (0.3–35.8 mg per 100 g), while caffeic acid (0.3–2.6 mg per 100 g) was detected in six species only. These natural plant phenolics could thus be a good source of antioxidants for applications in food.