Poly(3-hexylthiophene) (P3HT) hybrids with single-walled carbon nanotubes (SWNTs) were prepared using a series of SWNTs with various defect contents on their surfaces. The hybrids were synthesized by exploiting the π–π interaction between P3HT and the SWNTs, resulting in efficient dispersion of the carbon nanotubes in the P3HT solution. UV-visible and photoluminescence (PL) spectra showed that the carbon nanotubes quench the PL of P3HT in the hybrids, indicating that electron transfer occurs from photo-excited P3HT to the SWNTs. This electron transfer from P3HT to carbon nanotubes was disrupted by the presence of defects on the SWNT surfaces. However, the PL lifetime of P3HT in the hybrids was found to be the same as that of pure P3HT in solution, indicating the formation of a ground-state non-fluorescent complex of P3HT/SWNTs.