introduction: acmella ciliata (kunth) cass. is a native weed of northern south america known by its aliphatic alkamide content and used as an anesthetic and analgesic for toothache and sore throat. objective: to obtain, to analyze and to evaluate the biological activities of essential oils from acmella ciliata (kunth) cass flowers and leaves. methods: acmella ciliata essential oils were obtained by hydrodistillation and microwave-assisted hydrodistillation and analyzed by gas chromatography coupled to mass spectrometry. the biological activity of both essential oils was determined by using the modified agar-well diffusion assay, evaluating their activities against five bacteria and one fungus, along with tests of toxicity in artemia salina (lethal dose 50). results: microwave-assisted hydrodistillation was the technique with the best performances in the extraction of acmella ciliata. essential oils. their volatile fractions contain a high proportion of sesquiterpenes such as β-trans-caryophyllene, the major component. essential oils at two different concentrations (25 mg/ml and 15 mg/ml) showed a strong antimicrobial activity against gram-positive bacteria staphylococcus aureus and staphylococcus epidermidis, in addition they exhibited low toxicity against artemia salina, presenting mean lethal doses of 176, 156 and 100,104 ppm for the essential oils from leaves and flowers, respectively. conclusions: acmella ciliata essential oils are products with high content of terpenoids and marked antimicrobial activity against gram-positive bacteria (staphylococcus aureus and staphylococcus epidermidis) and low toxicity against artemia salina.