In this work, the comparative impact of iron oxide nanoparticles (synthesized by orange and green tea leaf extracts) on hydrogen production by three isolates of purple non-sulfur bacteria, Rhodobacter sphaeroides (MG588088), Rhodopseudomonas parapalustris (MH094546), and Rhodopseudomonas sp. TUT (MG813240) was investigated. UV-vis spectra showed that the absorption band centered at a wavelength of 550 nm, which corresponds to the surface plasmon resonances of synthesized FeNPs. Fourier transformed infrared spectroscopy spectrum (FTIR) exhibited the characteristic band assigned to Fe-O. Transmission Electron microscopy (TEM) image confirmed that the average size of NPs was 32-60 nm. Nitrogenase activity was significantly stimulated by iron oxide nanoparticle and the maximum activity was recorded at 150mg/L. The hydrogen yield was significantly enhanced by FeNPs. Iron oxide nanoparticles synthesized by green tea leaves extract were more stimulatory than those extracted from orange leaves extract.