Abstract The chemical composition of the volatile oils of Senna alata (Linn.) Roxb., Senna occidentalis (Linn.) Link and Senna hirsuta (Linn.) Irwin and Barneby (Fabaceae) were investigated. The oils were obtained by hydrodistillation and analyzed for their constituents by gas chromatography-mass spectrometry (GC-MS). Altogether, seventy three compounds were identified in the oils. The main components of S. alata essential oil were ar-turmerone (13.5 %), Î²-caryophyllene (7.3 %), (E)-phytol (7.0 %) and 6,10,14-trimethyl-2-pentadecanone (6.8 %). (E)-phytol (26.0 %), hexadecanoic acid (17.3 %), 6,10,14-trimethyl-2-pentadecanone (9.9 %) were the quantitatively significant constituents in S. occidentalis; while (E)-phytol (30.8 %) and pentadecanal (21.7 %) were the main components of S. hirsuta essential oil. The occurrence of (E)-phytol and 6,10,14-trimethyl-2-pentadecanone in the studied species may be of chemotaxonomic interest. Senna alata and S. occidentalis essential oils were found to be cytotoxic, inhibiting the growth of Hs 578T human tumor breast cell lines. However, all volatile oils displayed only moderate antimicrobial activities to the assayed standard strains of Bacillus cereus, Staphylococcus aureus, Pseudomonas aeroginosa, Escherichia coli, Candida albicans and Aspergillus niger.