Metal nanoparticles are a promising approach for the development of new antimicrobial systems. Silver nanoparticles (AgNP) have a significant antibacterial activity through bacterial surface adsorption and oxidative stress induction, as indicated by recent observations. This research aimed to use endophytic fungi from the genus Trichoderma spp. isolated from the Bertholletia excelsa (Brazil-nut) seeds and the soil to biosynthesize AgNPs and also test their antibacterial activity. The use of these fungi for this purpose not only valorizes the Amazon biodiversity but it also uses cleaner and cheaper processes, being part of the Green Chemistry concept. The particles were analyzed through Ultraviolet-Visible Spectroscopy and ZetaSizer and the band of absorption at 420 nm was analyzed through Localized Surface Plasmon Resonance. After characterization, the AgNP were tested for antibacterial activity against several bacterial strains, when it was observed that their antibacterial activity was superior in Gram-negative bacteria. [GRAPHICS] .