Pseudomonas aeruginosa is a dangerous bacterium causing nosocomial infections and difficult to treat because of its broad resistance to antibiotics. Siwak sticks, root of Arak tree (Salvadora persica) has been widely used since 7.000 years ago and has many benefits including antibacterial effect. Thus, research on whether siwak (Salvadora persica) stick extract has antibacterial effects need to be done by measuring the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). This experimental research was intended to explain such effect. This research used the dilution test of siwak (Salvadora persica) ethanol extract against Pseudomonas aeruginosa. Growth of bacteria on eleven different concentrations of each tube (80%, 70%, 60%, 50%, 40%, 20%, 10%, 5%, 2.5%, 1:25%, 0.625%) was observed by viewing tube clarity after incubation at 36 oC for 24 hours to measure the MIC. MBC was measured by the growth of bacteria on plates as a result of the bacteria cultivation from each tube. Replication was performed four times and the results were analyzed descriptively. In the MIC test, tubes with concentration of 80% to 20% were clear and tubes of 10% to 0.625% were cloudy. In MBC test, tube with concentration of 80% to 60% were not overgrown with bacteria and tube of 50% to 0.625% were overgrown with bacteria. In conclusion, MIC of siwak (Salvadora persica) stick extract against Pseudomonas aeruginosa is 20% and the MBC value of siwak (Salvadora persica) extract against Pseudomonas aeruginosa is 60%.