The present study describes for the first time a procedure for the radiolabeling of fullerene (C60) nanocrystals(nanoC60)with Na 125I, as well as the biodistribution of radiolabelednanoC60 (125I–nanoC60). Thesolvent exchange method with tetrahydrofuran was used to make colloidal water suspensions of radiolabelednanoC60 particles. The radiolabeling procedure with the addition ofNa 125I to tetrahydrofuranduring dissolution of C60 gave a higher radiochemical yield of radiolabelednanoC60 particles in comparison to the second option, in whichNa 125I was addedafter C60 was dissolved. Using photon correlation spectroscopy and transmission electron microscopy, 125I–nanoC60 particles were found to have a crystalline structure and a mean diameter of 200–250 nm. The 125I–nanoC60 had a particularly high affinity for human serum albumin, displaying95% binding efficiency after 1 h. Biodistribution studies of 125I–nanoC60 in rats indicated significant differences in tissue accumulation of 125I–nanoC60 and theradioactive tracer Na 125I. The higher accumulation of radiolabelednanoC60 was observed in liver and spleen, while accumulation in thyroid,stomach, lungs and intestines was significantly lower in comparison toNa 125I. In addition to being useful for testing the biological distribution ofnanoC60, the described radiolabeling procedure might have possible applications in cancerradiotherapy.