Pseudomonas aeruginosa is the most common agent causing bacterial pneumonia. This bacterium is classified as a nosocomial infection-causing bacteria, thus often experiencing antibiotic resistance. This research aims to determine the antibacterial effect of cajeput oil (Melaleuca leucadendra). The study follows an experimental laboratory approach with a posttest control group design. The method used is diffusion with Mueller Hinton agar as the medium. The results obtained from the diffusion test are in the form of the diameter of the inhibition zone. The diameter of the inhibition zone of cajeput oils antibacterial activity against Pseudomonas aeruginosa at concentrations of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% respectively are 15.73 mm 20.82 mm 17.91 mm 11.83 mm 11.25 mm 10.92 mm 10.46 mm 9.93 mm 9.57 mm. However, at 100% concentration, no inhibition zone was formed. The statistical analysis using the non-parametric Kruskal-Wallis test on the Pseudomonas aeruginosa group yielded p < 0.05, indicating an antibacterial effect at various concentrations of cajeput oil (Melaleuca Leucadendra) from micro, small, and medium enterprises (MSMEs) in Lamongan against Pseudomonas aeruginosa bacteria. The Man-Whitney tests analysis in this research indicates that cajeput oil (Melaleuca leucadendra) at concentrations of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% does not have a significant difference compared to the positive control (p > 0.05). Thus, cajeput oil (Melaleuca leucadendra) can substitute for the ability of ciprofloxacin in pneumonia treatment.