Highly-efficient CdS/CdSe quantum dots (QDs) co-sensitized solar cells based on sol-modified ZnO (SM-ZnO) photoanodes were structured. The influence of printing/annealing process on the crystallinity, morphology and thickness of SM-ZnO photoanode was investigated by X-ray diffraction and scanning electron microscopy (SEM). As revealed by the Raman spectra and diffuse reflection spectra, CdS and CdSe QDs can be loaded into SM-ZnO photoanode successfully and provide enhanced light absorption. By optimizing the CdS deposition cycle and the thickness of SM-ZnO photoanode, photovoltaic conversion efficiency as high as 2.64% under AM 1.5 illumination was obtained. Compared with ZnO-based QDSSC, the photovoltaic conversion efficiency of SM-ZnO-based QDSSC increased from 1.73% to 2.64%, which should be attributed to forming uniformly distributed ZnO nanocrystalline photoanode and thus exhibiting more efficient charge-transfer process, as evidenced from SEM. The sol-modification process is low-cost and easy to be carried out, which would attract a great deal of attention in DSSCs or QDSSCs.