In the present study, a bacterial strain isolated from a soil sample taken from the region around the root of the plant (Alhagi graecorum) that is growing in the desert west of the Sohag Governorate and molecularly identified as Streptomyces sp. was evaluated for the capability of selenium nanoparticles (SeNPs) production. The results showed that the bacterial strain could produce stable SeNPs sustainably within a week under optimized conditions (pH 7 and 32 °C) at its extra/intracellular wall. Subsequently, UV-Vis spectra were used to characterize SeNPs produced under different parameters, showing changes in the absorbance around 582 nm - 620 nm. The antimicrobial effects of SeNPs formed under different pH were also examined against pathogenic Escherichia coli. The results showed that SeNPs formed at acidic and basic pH induced substantially less antibacterial activity than those formed at a neutral pH where the diameter of the inhibition zone of SeNPs synthesized at pH 7 was 20 mm, but at pH 4 (13 mm), pH 5 (14 mm) and pH 9 (17 mm).