Alkaloid fractions isolated from Strychnos potatorum L.f. (Loganiaceae) seed were tested for their antimicrobial properties against some pathogenic gram positive, gram negative and acid-fast bacteria and fungi. These fractions have shown considerable antimicrobial activity against both bacteria and fungi at the tested concentrations (100 & 200 μg/mL). Further, the growth of Proteus vulgaris, taphylococcus aureus, Salmonella typhimurium, Vibrio cholerae, Mycobacterium tuberculosis, Aspergillus niger and Candida albicans were significantly inhibited. These findings have confirmed the use of this plant in treating of several microbial infections both in traditional and folk medicine in India.