Introduction: Chamomile (Chamaemelum nobile) is widely used throughout the world, and has anti-infl ammatory, deodorant, bacteriostatic, antimicrobial, carminative, sedative, antiseptic, anti-catarrhal, and spasmolytic properties. Because of the increasing incidence of drug-resistant bacteria, the development of natural antibacterial sources such as medical herbs for the treatment of infectious diseases is necessary. Extracts from different plant parts such as the leaves, fl owers, fruit, and bark of Combretum albifl orum, Laurus nobilis, and Sonchus oleraceus were found to possess anti-quorum sensing (QS) activities. In this study, we evaluated the effect of C. nobile against Pseudomonas aeruginosa biofi lm formation. Methods: The P. aeruginosa samples were isolated from patients with different types of infection, including wound infection, septicemia, and urinary tract infection. The fl owers of C. nobile were dried and the extract was removed using a rotary device and then dissolved in dimethyl sulfoxide at pH 7.4. The microdilution method was used to evaluate the minimum inhibitory concentration (MIC) of this extract on P. aeruginosa, and biofi lm inhibition was assayed. Results: Eighty percent of the isolated samples (16/20) could form a biofi lm, and most of these were isolated from wound infections. The biofi lm inhibitory concentration of the C. nobile extract was 6.25-25mg/ml, whereas the MIC was 12.5-50mg/ml. Conclusions: The anti-QS property of C. nobile may play an important role in its antibacterial activity, thus offering an additional strategy in the fi ght against bacterial infections. However, molecular investigation is required to explore the exact mechanisms of the antibacterial action and functions of this phytocompound.