rationale: polylepis australis bitter has a popular name that is que？oa or tabaquillo. its leaves and bark are traditionally used for infectious diseases in the respiratory pathways and other diseases in amaicha′s valley, in tucumán,. objectives: to evaluate the antimicrobial activity of ethanol extracts containing dry leaves and bark from p. australis against staphylococcus aureus and pseudomonas aeruginosa. methods: dry leaves and bark were soaked into 70 % alcohol for 5 days; afterwards, they were filtered, dried and sterilized. its antimicrobial activity was evaluated by agar plate diffusion method, and the effect of ph, bivalent cations and temperature on the antibacterial activity was determined. minimal concentrations were set such as inhibitory (mic), bacteriostatic (bsc) and bactericidal (mbc). the impact of ethanol extract on s aureus and p. aeruginosa morphology was analyzed by electronic transmission microscopy. the action of extracts on structural integrity and bacterial viability was elucidated through fluorescence. results: ethanol extract of dry leaves and bark from p. australis showed antimicrobial action against s. aureus and p. aeruginosa. the ethanol extract of bark presented with less antimicrobial activity than the leaf extract that was bactericidal against s. aureus and bacteriostatic against p. aeruginosa. the studied extract caused alterations in cytoplasmic membrane permeability of s. aureus, citosol loss and cell death. the treated p..aeruginosa culture showed blebs and vesicles in the outer membrane. conclusions: this research study validated the common use of the extract as an antimicrobial agent, mainly leaf extract.