Ag nanocubes decorated plasmonic TiO2 were synthesized by polyol method as a potential photocatalyst for photocatalytic hydrogen evolution. In this work, the Ag loading concentration on TiO2 was optimized for enhanced photocatalytic hydrogen evolution. Among different Ag loading, 1 wt% showed the highest hydrogen production capacity under solar irradiation due to elevated photon absorption in the presence of plasmonic Ag. Further, the influence of surface plasmon resonance of Ag nanocubes on TiO2 was also studied by tuning the Ag particle size and evaluating the photocatalytic hydrogen production under optimized Ag loading. The size of the Ag nanoparticles was varied using different molecular weight (Mw) PVPs as the size-directing agent. TEM analyses of the samples confirmed the formation of Ag nanocubes of various sizes in accordance with the PVPs used. Ag nanocube with a size of 15.98 nm showed the highest SPR effect, which enables higher photon absorption and could generate high photogenerated charge carriers for better photocatalytic reactions. The photocatalytic hydrogen production capacity of the above samples was evaluated under solar irradiation, and the sample with an Ag nanocube size of 15.98 nm showed a yield of 4258.40 μmol g-1 in 4 h, which is 12-fold higher than its pristine counterpart. This work illustrated the effect of Ag nanocube size for effective SPR and the transportation of this high energy towards host TiO2 for enhanced photocatalytic performance.