Free radicals react with biological molecules and destroy the structure of cells, which eventually causes free radical induced diseases such as cancer, liver disease, aging, etc. In this study, the total phenolic contents, 1, 1- diphenyl-2-picryl hydrazyl (DPPH^·) and OH^· radical scavenging activity and lipid peroxidation of 13 selected Egyptian plants were determined. Total phenolic contents of plant ethanolic extracts were measured as gallic acid. The antioxidant activities of plant ethanolic extracts at different levels (25, 50 and 100 μg/ ml) were evaluated using three complementary in vitro assays: inhibition of DPPH^· radical, hydroxyl radical and lipid peroxidation in liver homogenate mediated by FeSO₄/ ascorbate model system. The results showed that all plant ethanolic extracts increased antioxidant activities with increasing ethanolic extracts concentration. The ethanolic extracts of guava leaves, cinnamon bark and pomegranate peel significantly inhibited lipid peroxidation- induced by FeSO₄/ ascorbate model system, also have inhibitory effect on deoxyribose degradation. In addition, guava leaves had the highest free radical scavenging activity. These findings suggest that ethanolic extracts of guava leaves, cinnamon bark and pomegranate peel are powerful natural antioxidants and may be useful as antioxidants interest in the protection of biological system against various oxidative stresses. The chemical constitution of ethanolic extracts was investigated using gas chromatography–mass spectrometry (GC–MS) for the guava leaves and pomegranate peel. The ethanolic extracts were found to contain 19 and 23 components for guava leaves and pomegranate peel, respectively. The major peaks, identified by GC–MS, were 1,2-Benzenedicarboxylic acid, diisooctyl ester (28.72%), 5- Methyl-2-phenylindole (20.80%) and n-Octanoic acid (19.00%)for the guava leaves and 5-Hyroxymethyl- 2-formylfuran (68.35%), 2-Furancarboxaldehyde (6.94%) and 3,4-Dehydroproline (3.78%) for the pomegranate peel.