Iron and silver nanoparticles were synthesized using a rapid, single step, and completely green biosynthetic method employing aqueous sorghum extracts as both the reducing and capping agent. Silver ions were rapidly reduced by the aqueous sorghum bran extracts, leading to the formation of highly crystalline silver nanoparticles with an average diameter of 10 nm. The diffraction peaks were indexed to the face-centered cubic (fcc) phase of silver. The absorption spectra of colloidal silver nanoparticles showed a surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. Amorphous iron nanoparticles with an average diameter of 50 nm were formed instantaneously under ambient conditions. The reactivity of iron nanoparticles was tested by the H2O2-catalyzed degradation of bromothymol blue as a model organic contaminant.