Bacterial infection are currently life-threatening. From the discovery of Penicillin, series of antibiotics were formulated to kill different pathogenic bacteria due to the constant evolving of bacterial resistance. But then, the use and study of medicinal plants as antibiotic are still in progress, hence this study focused on the antibacterial effect of Allium fistulosum against Pseudomonas aeruginosa. Quantitative experimental research design were used in this study. Antimicrobial Susceptibility Testing were utilized to analyse the minimum inhibitory effect of the Allium fistulosum extract in different concentration against Meropenem and distilled water. It found out that there is no significant difference in the zone of inhibition of Pseudomonas aeruginosa treated with 100%, 75%, and 50% concentration of Allium fistulosum extract and positive control. Hence Allium fistulosum extract is not effective as antibacterial agent against Pseudomonas aeruginosa. The researchers recommend to further study the effectiveness of the plant extract to other pathogenic bacteria.