Abstract: Ziziphus spina-christi is a native plant growing in the warm and subtropical regions including Middle East. For a long time, its extracts have been used in alternative and complementary medicine with or without a scientific basis. The object of the present study was to evaluate the activity of Sidr plant hydro-methanolic extract against some microbes including Gram-positive, Gram-negative bacteria and Candida albicans using agar diffusion assay. The plant aerial parts yielded 5.7% of raw semisolid extract after maceration in hydro-methanol (50:50 v/v) and evaporation. Six concentrations (4, 8, 16, 32, 64 and 128 mg/mL in Muller-Hinton Broth) were used for the assay. The plant extract exhibited concentration-dependent activity against some Gram-positive bacteria, namely, Bacillus cereus (15.33 ± 0.52), Clostridium perfringens (12.33 ± 0.52), Listeria monocytogenes (11.17 ± 0.41) and Staphyllococcus aureus (10.17 ± 0.75); and against two Gram-negative bacteria, namely, Proteus vulgaris (8.5 ± 0.55) and Vibrio parahaemolyticus (8.33 ± 0.52); (the values are in mm after 128 mg/mL extract). The extract was without any visible activity against Enterococcus faecalis, Escherichia coli, Salmonella typhimurium, Shigella flexneri, Klebsiella aerogenes and Candida albicans. The minimum inhibitory concentrations (MICs) were 5.16 mg/mL (Bacillus cereus), 8.15 mg/mL (Listeria monocytogenes), 10.22 mg/mL (Clostridium perfringens), 13.71 mg/mL (Proteus vulgaris), 13.01 mg/mL (Vibrio parahaemolyticus) and 20.37 mg/mL (Staphyllococcus aureus). These data may indicate that Ziziphus plant extract is active against some pathogenic bacterial strains and thus may be useful in treatment of disease conditions caused by these bacteria. [Gheith I, El-Mahmoudy A. Assessment of the antimicrobial potential of the hydro-methanolic extract of Sidr (Ziziphus spina-christi) plant against selected pathogens in vitro. Life Sci J 2018;15(9):27-34]. ISSN: 1097-8135 (Print) / ISSN: 2372-613X (Online). http://www.lifesciencesite.com. 3. doi:10.7537/marslsj150918.03.