A simple, single-step, one pot method was developed for the synthesis of monodispersed, ultralow sized, water-dispersible, stable, positively charged gold nanoparticles using the branched polyethlyneimine (PEl) in an aqueous media. Sizes of the gold nanoparticles have been tuned by adjusting the concentration of PEl and the gold salt. Formation of gold nanoparticles has been evidenced using various characterization techniques such as quasi-elastic light scattering (QELS), transmission electron microscopy (TEM), x-ray diffraction (XRD), energy dispersive x-ray (EDX) and spectroscopy and UV-visible spectrophotometer.