The interest in water gas shift (WGS) reaction has grown significantly, as a result of the recent advances in fuel cell technology and the need to develop small-scale fuel processors. Recently, researchers have tried to overcome the disadvantages of the commercial WGS catalysts. As a consequence, supported Pt catalysts have attracted a lot of researchers due to high activity and stability for WGS at low temperatures. In this study, Pt-Na/Ce_(1-x)Zr_(x)O_2 catalysts with various Ce/Zr ratio have been applied to WGS at a gas hourly space velocity (GHSV) of 45,515 h^-1. According to TPR patterns of Pt-Na/Ce_(1-x)Zr_(x)O_2 catalysts, the reducibility increases with decreasing the ZrO_2 content. As a result, Cubic structure Pt-Na/Ce_(1-x)Zr_(x)O_2 catalysts exhibited higher CO conversion than tetragonal structure Pt-Na/Ce_(1-x)Zr_(x)O_2 catalysts. Expecially, Pt-Na/CeO_2 exhibited the highest CO conversion as well as 100% selectivity to CO_2. Moreover, Pt-Na/CeO_2 catalyst showed relatively stable activity with time on stream. The high activity of cubic structure Pt-Na/CeO_2 catalyst was correlated to its higher oxygen storage capacity (OSC) of CeO_2 and easier reducibility of Pt/CeO_2.