The method of successive ion layer adsorption and reaction was applied for the deposition of CdS nanoparticles onto a mesoporous In₂O₃ substrate. The filling of the nanopores in In₂O₃ films with CdS particles mainly occurs during the first 30 cycles of the SILAR deposition. The surface modification of In₂O₃ with CdS nanoparticles leads to the spectral sensitization of photoelectrochemical processes that manifests itself in a red shift of the long-wavelength edge in the photocurrent spectrum by 100–150 nm. Quantum-confinement effects lead to an increase of the bandgap from 2.49 to 2.68 eV when decreasing the number of SILAR cycles from 30 to 10. The spectral shift and the widening of the Raman line belonging to CdS evidences the lattice stress on the CdS/In₂O₃ interfaces and confirms the formation of a close contact between the nanoparticles.