Herein we report the surface modification of a CdS film by niobia nanoparticles via thioglycerol as an organic linker and thus fabricate an efficient and a stable photoanode for a photoelectrochemical (PEC) cell. We have synthesized three differenly sized (similar to 3, similar to 6 ,and similar to 9 nm) niobia nanoparticles by a hydrothermal synthesis approach and have further investigated the particle-size-dependent PEC performance of the nanoparticle-modified CdS photoanode. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirm the formation of Nb2O5 nanoparticles that are prepared via decomposition of the niobium peroxo complex during the hydrothermal reaction and reveal the presence of surface OH- groups over niobia nanoparticles that impart a high catalytic property to a material. The nano-Nb2O5-modified photoanode displayed a 23-fold higher power conversion efficiency compared to that of CdS. This modified structure increases the open circuit voltage (OCV) from 0.65 to 0.77 V, which is attributed to the nano-Nb2O5-induced surface passivation effect over bare CdS. Linking of nanoparticles on the CdS surface improves the photocorrosion stability of the CdS photoanode for even longer than 4 h in contrast to the tens of minutes for the base CdS surface. The uniform coverage of the CdS photoanode surface by niobia nanoparticles is thus found to be the controlling parameter for achieving a higher PEC performance and stability of the photoanode. This finding directed us to design an improved CdS photoanode for efficient and prolonged PEC hydrogen generation from a PEC cell.