Background: The spread of drug resistant pathogens is one of the most serious threats to successful treatment of microbial infections. However, in the recent time, unrelenting effort to explore the medicinal importance of plants has become a major concern to scientists because of the less toxic and reliable phytopharmacoactive components of these plants. Purpose: The present study was carried out to evaluate the growth inhibitory effect of the volatile oil of Syzygium samarangense leaves against Proteus vulgaris and to examine the mode of inhibition of this oil on partially purified extracellular protease of this pathogen. Procedures: The volatile oil was extracted by hydrodistillation from air-dried leaves of Syzygium samarangense. The inhibitory effect of the oil was tested against the growth of Proteus vulgaris under favourable conditions using spectrophotometric method in nutrient broth. Similarly, the mode of inhibition against partially purified and characterized extracellular protease of this nosocomial opportunistic enteric pathogen was determined from Lineweaver Burke plot. The activity of this protease was also assessed based on the effect of different chloride salt solutions. Findings: The volatile oil of Syzygium samarangense inhibited Proteus vulgaris with IC50 of 0.42%v/v. The enzyme had optimum activity at pH 7.5 and 45°C. This enzyme was relatively stable at pH range of 7.0 - 8.0. The activity of this enzyme was moderately activated by K+ but most inhibited by Co2+. Double reciprocal plot of this enzyme showed a competitive inhibition by the volatile oil with Vmax of 8.33 x 103μmol/min and the K m in the absence and presence of volatile oil were 0.23mg/ml and 1.25mg/ml respectively. Highest percentage yield was 35.9 while the highest purification fold was 4.49. Conclusion: This study has shown that the relative stability of the protease between pH 7.0 – 8.0 confirmed one of the reasons why this pathogen is responsible for most of the urinary tract infections. The volatile oil extracted from the leaves of Syzygium samarangense possessed antimicrobial activity and its inhibition on the extracellular protease of Proteus vulgaris may just be one of its numerous modes of antibacterial activity.