THE PRESENT study focused on the biosynthesis of silver nanoparticles using the ethanolic extract of the green alga Ulva fasciata (green algae). The synthesized silver nanoparticles were characterized by UV-Vis spectra, TEM (Transmission Electron Microscope) and FT-IR analysis. The absorption spectra of the formed AgNPs was observed at 350 nm, while the FT-IR spectrum revealed a presence of bands at about 2076.96 and 1840.72 cm-1. On the other hand, TEM analysis , exhibited spherical and rod shaped AgNPs with size range of 2 to 200 nm. The chemical constituents, fatty acids, alkaloids, phenolic compounds, terpenoids, aromatic compounds of studied algal extracts were identified by GC-MS. The Gas chromatography-mass spectrometry (GC-MS) analysis of the green alga Ulva fasciata ethanolic extract showed a presence of fatty acids, alkaloids, phenolic, terpenoid and aromatic compounds. Potential activity test of the AgNPs formed by Ulva fasciata ethanolic extract against the nephrotoxicity on albino rats revealed good positive results indicated the preventive effects of the disease by using of Ulva fasciata AgNPs.