Worldwide, bacterial resistance is a public health problem, being one of the main causes of therapeutic failure in infectious diseases. The objective of the present study was to determine the in vitro antibacterial activity of Alchornea triplinervia (Sprengel) Muell Arg "zancudo caspi" against Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 and clinical isolates, and to identify the secondary metabolites in leaves and bark, through phytochemical screening. For phytochemical screening, the method of Chhabra, et al. Adapted and for antibacterial activity, the Disc Diffusion method (Kirby-Bauer) and CMI. The yield obtained was: leaf 11.88% and bark 3.22%. In the phytochemical screening, the presence of phenols, tannins, flavonoids, steroidal triterpenes and saponins was found; In the antibacterial activity according to the inhibition halo,...