The research utilized extracellular polysaccharides of Bacillus velezensis Y12 to synthesize silver nanoparticles (EPSY12-Ag nanoparticles， EPSY12-AgNPs)， and the physiochemical as well as the biological characteristics of the EPSY12-AgNPs were evaluated. The findings demonstrated that the premium conditions for EPSY12-AgNPs synthesis were using 5 mg/mL of extracellular polysaccharide， 10 mmol/L of silver nitrate solution， at pH 12. The EPSY12-AgNPs were spherical， carried a negative charge， and distributed evenly. The particle sizes varied between 40 nm and 50 nm. The antibacterial tests demonstrated that the substances displayed different levels of inhibitory activity against Staphylococcus aureus， Escherichia coli， Acinetobacter， Staphylococcus saprophyticus， Bacillus cereus， and Hafnia alvei. The most potent inhibitory effect was observed against S. saprophyticus， resulting in an inhibition zone measuring (16.568 ± 0.340) mm. EPSY12-AgNPs effectively inhibit the biofilm of H. alvei， achieving a remarkable inhibition rate of 45.37% when used at a dose of 20 μg/mL. EPSY12-AgNPs also demonstrated varying levels of antioxidant activity against ABTS radical， DPPH radical， and superoxide anions， as indicated by antioxidant assays.