Nanoparticles (NPs) are used in many fields. For example, electronics, optics, textiles, pharmaceuticals, catalysts, water treatment, and environmental remediation. In this work, the biosynthesis of silver nanoparticles (Af-AgNPs) from Astragalus flavesces leaf was synthesized. Af-AgNPs were featured by UV–visible, Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, and powdered X-ray diffraction (XRD) analyses. The maximum absorption peak was detected at 417 nm. The average size of Af-AgNPs was 63.15 nm and their spherical shape was determined by SEM spectral analysis. XRD spectral analysis at 2θ degrees of 38.1°, 44.3°, 64.4°, and 77.4° can be indexed to the (111), (200), (220), and (311) face-centered cubic crystalline structure. Af-AgNPs have the potential of − 29.1 mV which indicated the stability of nanoparticles as well as repulsion among the particles. Antioxidant activities of Af-AgNPs and the extract were investigated by the DPPH^·, ABTS^·+, and FRAP assays. Af-AgNPs showed antioxidant activity to a degree that can be used in the food and pharmaceutical industries. The catalytic activity of Af-AgNPs was studied and at 28 h, 69% degradation was observed in the methylene blue solution.