AbstractThe chemical composition of the hydrodistilled oils of the leaves of Psidium guajava L. (guava leaf) and Psidium cattleianum Sabine (strawberry guava) was determined by GC/MS analysis to identify their chemotypes. Moreover, in vitro antimicrobial activity of these volatile oils against selected bacteria, yeast, and mycelia fungi was studied. The yield of the volatile oil hydrodistilled from the leaves of P. guajava L. and P. cattleianum Sabine was 1.6 and 2.69g/kg on fresh weight basis, respectively. Limonene was the major identified hydrocarbon in P. guava leaves’ oil (54.70%), whereas, 1, 8-cineole was the major identified oxygenated monoterpenoid (32.14%) in common guava leaves. The foliar oil of P. cattleianum was predominated by the sesquiterpene hydrocarbon; β-caryophyllene representing 28.83% of the total oil make-up. The antibacterial activity of guava leaf oil was more pronounced against Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa than that of strawberry guava leaves, while P. cattleianum showed a higher activity against ess. The MIC of the volatile oil of the leaves of P. guajava against S. aureus was 6.75μg/ml, while that of P. cattleianum exhibited MIC value of 13.01μg/ml against Neisseria gonorrhoeae. Results demonstrated that the volatile oil of both Psidium species showed different chemotypes. Moreover, the volatile oils of guava and strawberry guava leaves might be good candidates as antimicrobial agents.