Two different strains of yeast, Saccharomyces cerevisiae, AP22 and CCFY-100 were studied for bioaccumulation of gold in the form of H198AuCl4. Thin sectioning and subsequent study by transmission electron microscopy (TEM) reveals that Au3+ was in situ reduced to Au(0) and nano sized gold particles were formed inside the cell. Very low dose γ-energy being responsible for reduction of cationic gold in the polymeric cytoplasm matrix. The formation and entry of gold nanoparticles in the yeast cells were studied as a function of time at certain intervals starting from 15min to 72h. The gold nanoparticles gradually moved inward as a function of time from cell wall to cytoplasm to nucleus and finally accumulated in the nucleolus of the cell. TEM image of budding yeast shows that gold nanoparticles are not transferred to the new generation yeast cells. © 2011 Elsevier B.V.