The oxidative effect of carbon nanodispersions on protein has been studied through comparative examination of the spontaneous transition of hemoglobin oxy-form with the heme iron in reduced state Fe(II) into the physiologically inactive met-form with the heme iron in oxidized state Fe(III) (autooxidation) in aqueous dispersions of three nanocarbon types – fullerene C₆₀, nanodiamonds, and shungite nanocarbon (ShC). Unlike nanodiamonds, C₆₀ and ShC have been shown to act as prooxidants in hemoglobin solution since their presence can provide for acceleration of the oxidation reaction of the heme iron in hemoglobin and for steady transition of a considerable part of hemoglobin from the oxy to the met-form. The effect of carbon nanoparticles on the process of protonation of distal histidine, but not on the monomer-dimer-tetramer equilibrium of hemoglobin in aqueous dispersion has been suggested as a probable mechanism of the oxidation activity of the nanoparticles in the protein.