Introduction: Cnidoscolus quercifolius Pohl (Euphorbiaceae) is a Brazilian medicinal plant, popularly known as “favela”, “faveleira” and “urtiga-branca”. In folk medicine, its leaves and stem barks are used to treat urinary tract infections. In this study, we report the isolation and characterization of a mixture of two lupane-type triterpenes and one bis-nor-diterpene from the hexane extract of the stem barks. Methods: An aliquot of hexane extract was fractioned by means silica gel chromatography column, yielding a mixture of two compounds (1 and 2). Compound 3 was obtained from the chloroform subfraction through preparative thin layer chromatography (TLC). The compounds were identified by comparison of their spectroscopic data to those reported in the literature. The antibacterial activity of these compounds was evaluated by the microdilution method, through determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), using gram-positive (E. faecalis and S. aureus) and gram-negative (E. coli, K. pneumoniae and S. marcescens) strains. Results: The chemical constituents were identified as a mixture of lupeol-3β-O-cinnamate (1) and lupeol-3β-O-dihydrocinnamate (2) and, phyllacanthone (3). Compounds 1/2 and 3 showed a bacteriostatic effect ten and twenty times higher (MIC = 0.5 and 0.25 mg.ml-1, respectively) than the hexane extract, respectively (MIC = 5.0 mg.ml-1). The molecules also showed a relevant bactericidal effect, mainly compound 3 (MBC = 0.25 mg.ml-1). Conclusion: These results suggest that C. quercifolius may be considered a promising source of new antibacterial agents. In addition, this investigation supports the medicinal use of this plant for the treatment of urinary tract infections.