In recent years, a substantial amount of evidence has pointed to the key role of free radicals and other oxidants as the main culprits for aging and degenerative diseases associated with aging, such as cancer, cardiovascular diseases, cataract, decline of the immune system and brain dysfunctions. The objective of this work was therefore to detect variations in total phenol and flavonoid content, and in the antioxidant activity of samples of Stachytarpheta cayennensis. Dried and crushed samples were submitted to static maceration extraction to obtain the hexane, ethyl acetate and ethanol fractions. Phytochemical prospecting and an assessment of the content of phenolic constituents and of the antioxidant activity were carried out. The data was analyzed according to the mean ± standard deviation and submitted to analysis of variance followed by Tukey’s test to establish the degree of significance (p < 0.05). Flavonoids, tannins, coumarins, terpenoids and steroids, alkaloids and anthraquinones were detected in the samples. The content of total flavonoids varied between 2.69 ± 0.49 and 6.21 ± 0.67 g/100 g, while the total phenols ranged from 1.83 ± 0.06 to 15.33 ± 0 .44 g/100 g. The extracts produced EC50 between 38.60 ± 5.42 and 288.44 ± 22.12 μg/ml. The results indicate that the use of solvents of different polarities in the extraction process is an important strategy to detect variations in the levels of total phenols and flavonoids, and of antioxidant activity, in samples of S. cayennensis. Key words: Phenols, flavonoids, free radicals, secondary metabolites.