In this paper, the physical, optical, and magnetic properties of the Selenium-doped Zinc Oxide/Silver Oxide/Iron (III) Oxide (Se-doped ZnO/Ag2O/Fe3O4) nanocomposite were studied. The nanocomposite was synthesized through the green method with Sclerorhachis Leptoclada extract and then characterized by XRD, FT-IR, FESEM, EDX, DRS, AFM, and VSM. The analyses of XRD and FESEM show the crystal structure and spherical morphology, moreover, the outcomes of EDX verified the presence of Zn, Ag, Fe, Se, and O elements. According to VSM analysis, the nanocomposite has a superparamagnetic property. The results of the photocatalytic test displayed that the degradation percentage of methylene blue (MB) dye in pH =10, nanocomposite amount ∼ 30 mg, and dye concentration ∼ 0.5×10−3 M was about 99%.