Nanobiotechnology represents an economic alternative for chemical and physical methods of nanoparticles formation. The objectives of this study were to synthesize selenium nanoparticles by microbial processes using anaerobic metal-reducing bacteria as well as to characterize mineralogical properties of the nanoparticles. The selenium nanoparticles were about 200 nm in size and ball shaped. Microbial processes for elemental selenium synthesis may be useful for recovery of natural selenate in the natural environments and immobilization of selenium isotope in the high level nuclear waste disposal sites.