Chlorophyll (Chl) was immobilized into a 1,4-butanediol-modified MCM-41 (BMCM-41) intercalated by poly(3-hexylthiophene) (P3HT) to form BMCM-41/P3HT/Chl nanocomposites having P3HT contents of 10, 30, 60, and 90 wt % from a solution-casting method. Wide-angle X-ray diffraction and transmission electron microscopy studies indicate that the pore structure of MCM-41 was retained after surface modification and a subsequent P3HT intercalation process. Scanning electron microscopy images showed that the BMCM-41 nanoparticles dispersed into the polymer matrix of BMCM-41/P3HT/Chl, and the sample with 10 wt % P3HT content gives the most homogeneous nanoparticle dispersion. Nitrogen adsorption-desorption results confirmed that the P3HT intercalation and Chl immobilization inside the BMCM-41 mesopore were successfully carried out. The pore volume and surface area of BMCM-41 decreased significantly when the amount of P3HT was increased from 10 to 90 wt %. The UV-vis study showed a blue shift of the pi-pi* transition band of P3HT in the spectra of BMCM-41/P3HT/Chl nanocomposites. The FT-IR study indicates an increase of the thiophene ring stretching and a decrease of the C horizontal lineO stretching when P3HT and Chl were inside the mesopore. The photovoltaic property of Chl-doped P3HT was improved significantly upon the addition of BMCM-41 nanoparticles, and BMCM-41/P3HT-10/Chl exhibits the highest incident photon-to-current conversion efficiency of 7.16%.