Single-wall carbon nanotubes (SWCNTs) are attractive components for nanoscale electronics, however their optoelectronic properties have been limited by the optical characteristics of semiconducting SWCNTs. To enhance the functionalities of SWCNTs, beta-carotene was encapsulated in SWCNTs and its light-harvesting function was investigated. The detailed structure of encapsulated beta-carotene was clarified using x-ray diffraction and the polarization dependence of the optical absorption spectra. The photoluminescence spectra revealed excited energy transfer from beta-carotene to the SWCNTs.