The antimicrobial and antioxidant activities and the composition of the essential oil and of the supercritical extracts of Xanthium strumarium were studied. The best yields were observed in the supercritical extracts (SFE). The composition of the extracts obtained by SFE and by hydrodistillation presented little qualitative difference, but they did differ quantitatively. The essential oil contained a high content of beta-guaiene (79.6%) while as the major compounds in the supercritical extracts were unidentifiable compound with Kovats Index of 2303 and xanthinin. All the X. strumarium extracts showed strong antimicrobial activity against Staphylococcus aureus, Escherichia coli, Salmonella thyphimurium, Pseudomonas aeruginosa and Clostridium perfringens, however no differences were observed between the extracts. Poor antioxidant activity was found for all the Xanthium strumarium extracts.225424429