Abstract: In this study, a novel strain with high Na₂SeO₃ reducing ability was screened from marine strains, providing a new reduction system for the biosynthesis of Se nanoparticles (SeNPs). Firstly, 41 marine strains from Arctic Ocean sediments were screened, and a strain with high selenium-tolerant was obtained and species identified. Subsequently, the screened marine strain was used for the biosynthesis SeNPs and the SeNPs were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and particle size analysis. Furthermore, the antibacterial activities of SeNPs were also determined. The results showed that strain 72 had the strongest tolerance to Na₂SeO₃, which could grow in the presence of 300 mmol/L Na₂SeO₃ and reducing it to brick red SeNPs. Subsequently, strain 72 was identified and named as Bacillus sp. Q72. The SeNPs biosynthesized by this strain were spherical particles with an average size of 169.3 nm and a potential of −48.1±0.5 mV. There were amino and hydroxyl groups on their surface. The SeNPs produced by Bacillus sp. Q72 showed better inhibitory activity against E. coli. When the concentration of SeNPs was 200 μg/mL, the inhibitory rate against E. coli reached 92.1%.