Abstract: Aims: The stability of solutions of fullerene C60 with human serum albumin (C60/HSA) has not been studied in detail. In this study, we report on the preparation of stable C60/HSA solutions that are formed via the formation of C60/HP-β-CyD nanoparticles, i.e. by transferring C60 molecules from HP-β-CyD to HSA molecules, and an investigation of the reactive oxygen species on the behavior of the resulting C60/HSA. Main methods: Structural and functional properties were examined by spectroscopic techniques, including circular dichroism (CD), fluorescent spectra (FI), and electron spin resonance spin-trapping method, and by cell viability test using A549 cells. Key finding: Aqueous C60/HSA solutions with a small distribution size, excellent dispersion stability and a high dispersion concentration were obtained without the use of organic solvents. CD and FI spectra indicated that the HSA had undergone structural changes as the result of C60/HSA formation. Binding experiments indicated that C60/HSA had increased Site I and Site II-ligand binding capabilities. The HSA, in the form of C60/HSA was, therefore, conformationally altered, and its binding capabilities were enhanced. Radical scavenging studies using the 1,1′-diphenyl-2-picrylhydrazyl radical showed that C60/HSA had an increased antioxidant activity, compared to HSA alone. Further, C60/HSA efficiently generated not only superoxide anion radicals O2 ·− but also singlet oxygen 1O2 through photoirradiation. C60/HSA showed cell toxicity characteristics after light irradiation, but no toxicity was observed in the absence of irradiation. Significance: C60/HSA not only has an excellent stability and antioxidant activity, but also has substantial phototoxicity properties. It thus appears that HSA can be used as a carrier of C60 in drug delivery systems for photodynamic therapy. [Copyright &y& Elsevier]