Recently, nanomaterials have attracted significant attention due to their unique properties. Nanoparticles possess advantages such as small particle size and large specific surface area, which can effectively alter the wettability of rock formations and exhibit significant application potential in enhancing oil recovery in oilfields. This study aims to characterize biosynthesized nanoparticles and evaluate their capability for enhanced oil recovery. In this study, Ag+ was reduced to Ag0 by Scenedesmus extract to synthesize Ag NPs. The bio-synthesized Ag NPs were characterized by laser particle sizer, ultraviolet-visible(UV-vis) spectrophotometer, Fourier transform infrared spectroscopy(FT-IR), Zeta potentiometer, Energy-dispersive X-ray spectroscopy (EDX) and Scanning electron microscopy(SEM). Furthermore, their ability to alter the wettability of rock formations was evaluated. Physical oil displacement simulation experiments were conducted to assess their effectiveness in enhancing oil recovery. The results demonstrated that the bio-synthesized Ag NPs were small spherical and elliptical particles with the size between 20~50 nm. The average zeta-potential of the silver nanoparticle system was measured at -21.2 mV, confirming its favorable stability in the reaction medium system. The contact angle on glass slides treated with 600 mg/L silver nanofluid was decreased from 142° to 68°. The bio-nano system combined with rhamnolipid achieved an oil-water interfacial tension of 0.018 mN/m. In low-permeability cores with a permeability of 25×10?3 μm2, the oil displacement efficiency would further enhanced by 15.47% compared with water flooding. Micro-model experiments demonstrated that the bio-nano system can effectively mobilize residual oil after primary water flooding, thereby enhancing crude oil recovery.