In most of the studies, toxic and harmful reducing agents were used for the chemical reduction of graphene oxide (GO) and into reduced graphene oxide (rGO). Here, onion juice is used as a natural and green reducing agent for the reduction of GO into rGO. The effect of onion juice concentration and reaction temperature on the reduction ability of onion juice have been studied. The present synthesis approach avoids the use of toxic and harmful chemicals for reduction of GO. The mechanism of reduction of GO at various concentrations of onion juice is explained in terms of presence of cysteine in the onion juice as one of the chemical constituents. The X-ray diffraction (XRD) results revealed the high degree of reduction with superior quality. Transmission electron microscopy (TEM) images provide clear evidence for the formation of transparent and thin layers of graphene. We have extended our analysis to reveal the quality of rGO produced by onion juice assisted reduction of GO using D, G and 2D bands present in the Raman spectra. Moreover, we have discussed the role of onion juice concentration and reaction temperature on evolution of D and G bands and ID/IG ratio, which in turn tell the overall growth of graphene sheet. Fourier transforms infrared spectroscopy (FTIR) measurements also show significant degree of reduction of GO. The UV-Vis. absorption spectrum further confirms the ability of onion juice to reduce GO into rGO. The synthesized product shows good dispersibility in aqueous solvent. Thus, the present report provides a green and facile approach for the synthesis of graphene derivatives with enormous potential.