Blackstonia grandiflora (Viv.) Maire is a medicinal plant used in Algerian traditional medicine as a natural remedy to treat fever. Two compounds were isolated from aerial parts of Blackstonia grandiflora, halenaquinone (1) and gentiopicroside (2), The structures of the isolated compounds were determined by CPG-MS, 1D- and 2D-NMR techniques. The dichloromethane, ethyl acetate and n-butanol (CH2Cl2, EtOAc and n-BuOH respectively) extracts were evaluated for in vitro antibacterial activity and to determine the zone inhibition of extracts on some bacterial strains, the antibacterial activity were tested against two gram negative (Pseudomonas aeruginosa, Escherichia coli) and two gram positive (Staphylococcus aureus, Bacillus sp) bacterial strains using diffusion method. The results indicated a good inhibition of EtOAc extract on the growth of gram negative bacteria. Furthermore, CH2Cl2 extract showed a significant inhibitory effect against gram positive bacteria.