Abstract: The recent development in the antimicrobial therapy to meet the challenges of resistant pathogenic bacteria has called for rapid growth in exploring natural products as alternative. The antimicrobial activity of the oils from the leaf and stem of Chromolaena odorata against nine enteric pathogenic bacteria was assessed and compared with commonly used antibiotics. Specifically, we examined the mode of inhibition of these oils on the extracellular protease of Pseudomonas aeruginosa. The inhibition zones of the oils range from 13.0±1.0-43.5±2.5 mm in Salmonella paratyphimurium and Shigella dysenteriae, respectively. Ceftriaxone has the highest inhibition of 26.0±2.0 mm against Salmonella paratyphimurium. There was a significant difference (p<0.05) between the average inhibition of the antibiotics, 5.0±0.82 mm and the volatile oils, 18.0±4.0 mm. Each of the microbes was sensitive to at least one of the oils. The extracellular protease of Pseudomonas aeruginosa had optimal activities at pH 7.5 and 35°C. The volatile oils competitively inhibited the extracellular protease of Pseudomonas aeruginosa with Vmax = 0.91 μmol min-1 and Km = 0.48 mg mL-1 (oil absent) but the K'm increased to 0.93 and 1.25 mg mL-1 in the presence of the volatile oils of the leaf and stem of this plant, respectively. The highest purification fold of 2.35 (6.92 μmol min-1 mg-1 protein) was achieved from the crude enzyme with DEAE anion exchange chromatography. The chromatographic peaks may be an evidence of multiple subunits of this enzyme. Therefore, the oil of Chromolaena odorata possessed antimicrobial activity and its ability to inhibit extracellular protease of Pseudomonas aeruginosa will be a possible source of nutraceuticals for clinical purpose.