We report the synthesis and characterization of C60@SWCNT peapods and double-walled carbon nanotubes (DWCNTs) derived from the peapods. Single-walled carbon nanotubes (SWCNTs), C60@SWCNT peapods, and DWCNTs were characterized by Raman and optical spectroscopy. The radial breathing modes (RBMs) of the tubes in C60@SWCNT peapods are shifted to higher energies compared to the RBMs in SWCNTs, while in the case of DWCNTs the RBMs related to the outer tubes are shifted to lower energies compared to SWCNTs. A similar trend is observed for the absorption bands. These results suggest that the filling of the SWCNTs with C60 molecules decreases the average diameter of the electron cloud around the tubes, whereas the filling with an inner tube increases it.