Pt on ceria catalysts for water-gas shift (WGS) reaction were prepared by employing three ceria nanopowders synthesized with different processing techniques and having different surface area and porosities. Nano-Pt (∼0.5-2 nm) was deposited in the vapor phase onto each of the three ceria supports by Reactive Spray Deposition Technology (RSDT). The catalysts were performance tested for the WGS reaction in the temperature range of 150-450 °C at a gas hourly space velocity (GHSV) of 13,360 h-1. The structure-activity relationship for the ceria-based materials was studied. The most promising catalyst was Pt supported on mesoporous ceria with crystallite size of 5.8 nm and Brunauer-Emmett-Teller (BET) surface area of 187 m2/g. This configuration demonstrated complete CO conversion at 225 °C. The CO adsorption strength and the ability to dissociate H2O are the two main factors that determine the activity of a particular catalyst site for the water-gas shift (WGS) reaction. This study leads to the conclusion that the highest water-gas shift reaction activity was obtained on Pt supported on the mesoporous ceria with low crystallite size and high surface area, with well dispersed Pt, leading to enhanced Pt-ceria interaction.