Seasonal variation of the oil composition and biological activities from aerial parts of Achyrocline satureoides were investigated. Essential oils were analysed by gas crhromatography-mass spectrometry (GC-MS) after hydrodestillation. Results exhibited maximum amounts of hydrodistilled essential oils in spring (0.10 %; m/m). The compounds α-pinene (28.5-41.7 %) and (E)-caryophyllene (29.8-38.5 %) were the most abundant component in all seasons. Antimicrobial activity measurement of minimum inhibitory concentration (MIC) varied significantly (p < 0.05). It was more significant in autumn (37.9 μg/mL) and winter (38.4 μg/mL) than other seasons against bacterial strains Staphylococcus epidermidis ATCC11228. MIC against bacterial strains Bacillus cereus ATCC11778 was 37.9 μg/mL (autumn) and 76.8 μg/mL (winter) and 37.9 μg/mL (autumn) and 76.8 μg/mL (winter) against bacterial strains Klebsiella pneumoniae ATCC13883. The results showed that yield, chemical composition and antimicrobial activity of essential oil of Achyrocline satureoides (Lam) D.C changed according to the plant collection period.Colegio de Farmacéuticos de la Provincia de Buenos Aire