Gold@carbon dots composite nanoparticles (Au@CDs) with ultrathin carbon dot (CD) shells of ca. 2 nm were prepared by reducing HAuCl(4) with CDs at 100 °C. By adjusting the feeding mass ratio of HAuCl(4) to CDs, the average diameters of Au@CDs can be modulated from 8 to 44 nm. The suspension of Au@CDs with an average diameter of ca. 24 nm was applied as a substrate for surface enhanced Raman scattering (SERS) and it exhibited a higher SERS effect for rhodamine 6G (Rh6G) than the suspension of pure Au nanoparticles with nearly the same size. The excellent SERS effect of Au@CDs is mainly attributed to their improved capability of adsorbing the aromatic probe molecules.