Density change of single-walled carbon nanotubes (SWCNTs) with tetrachloroaurate enables chirality sorting of the SWCNTs. In this study, we examined in detail about the density change behavior of individually solubilized (n,m)-SWCNTs caused by tetrachloroaurate using density gradients centrifugation and vis-near IR absorption spectroscopy. The (7,5)-, (8,4)- and (8,3)- SWCNTs showed a linear relationship between the density and the degree of the oxidation of the corresponding SWCNTs. Although the (6,5)-SWCNTs was hardly oxidized by tetrachloroaurate, their density increased by the addition of tetrachloroaurate.