Gold nanorod dimers were prepared in aqueous solution. The nanorod dimers were separated from other nanorod assemblies by a stepwise density-gradient centrifugation using sucrose (20, 30, 40, 50, and 60% w/w). The centrifugation step (3400 x g, 20 min) produced two bands, a side-wall sediment, and a bottom precipitate. The topmost band contained nanorod monomers. The bottom precipitate was redispersed in water, and its surface plasmon band was consistent with that of a theoretical model of a nanorod dimer. Thus, density gradient centrifugation is effective in fractionizing nanorod dimers.