Objectives To demonstrate biotransformation of toxic Cr(VI) ions into Cr2O3 nanoparticles by the yeast Schwanniomyces occidentalis. Results Reaction mixtures containing S. occidentalis NCIM 3459 and Cr(VI) ions that were initially yellow turned green after 48 h incubation. The coloration was due to the synthesis of chromium (III) oxide nanoparticles (Cr(2)O(3)NPs). UV-Visible spectra of the reaction mixtures showed peaks at 445 and 600 nm indicating (4)A(2g) -> T-4(1g) and (4)A(2g) -> T-4(2g) transitions in Cr2O3, respectively. FTIR profiles suggested the involvement of carboxyl and amide groups in nanoparticle synthesis and stabilization. The Cr(2)O(3)NPs ranged between 10 and 60 nm. Their crystalline nature was evident from the selective area electron diffraction and X-ray diffraction patterns. Energy dispersive spectra confirmed the chemical composition of the nanoparticles. These biogenic nanoparticles could find applications in different fields. Conclusions S. occidentalis mediated biotransformation of toxic Cr(VI) ions into crystalline extracellular Cr(2)O(3)NPs under benign conditions.