Aims:The anti-bacterial effect of some selected Samburu medicinal plants were evaluated on bacterial strains like Staphylococcus aureus-ATCC 20591, Bacillus subtillis-local isolate, Salmonella typhi-ATCC 2202, Escherichia coli-STD-25922 and Pseudomonas aeruginosa-ATCC 25852. Methodology and Results: Methanol was used as an extraction solvent for the medicinal plants after they had been dried and ground using the laboratory grinding miller. The in vitro anti-bacterial activity was performed by agar disc diffusion method. The significant anti-microbial activity of active extracts was compared with the standard antibiotics, cefrodoxima and amoxicillin. These results were significant at p < 0.01. The MICs were also determined by the micro titre-plate method. The MICs of the most active plants ranged from 18.75 mg/mL to 37.5 mg/mL. The MBCs ranged between 18.75 mg/mL to 37.5 mg/mL. The most active plant that had substantial activity in at least all the test cultures was found to be Lannea triphylla (A.Rich) Engl. A number of phytochemicals were also found to be present with tannins being the most abundant followed by flavonoids and saponins. Conclusion, significance and impact of study: The findings show that most of the medicinal plants used by the Samburu community have some significant activity on the bacterial isolates known to cause diarrhoea.