The stem bark of the Brazilian medicinal plant Zizyphus joazeiro C. Mart. was phytochemically investigated. Three known compounds (betulinic, ursolic and alphitolic acid) and three new derivatives of betulinic acid, 7β-(4-hydroxybenzoyloxy)-betulinic acid, 7β-(4-hydroxy-3′-methoxybenzoyloxy)-betulinic acid and 27-(4-hydroxy-3′-methoxybenzoyloxy)-betulinic acid which showed a considerable activity against Gram-positive bacteria were isolated from the dichloromethane extract. The structures were established on the basis of NMR spectroscopy and mass spectrometry.