A comparative study on nano-sized Pt/Ce0.8Zr0.2O2 and Pt/Ce0.2Zr0.8O2 catalysts in a single stage water gas shift (WGS) reaction was carried out. These catalysts were prepared by impregnating 1 wt% Pt on nano-sized cubic (Ce0.8Zr0.2O2) and tetragonal (Ce0.2Zr0.8O2) supports. Both catalysts have been applied to WGS under identical conditions to understand beneficial effect of cubic/tetragonal phases of Ce(1 - x)Zr(x)O2. 1 wt% Pt/Ce0.8Zr0.2O2 exhibited higher CO conversion than 1 wt% Pt/Ce0.2Zr0.8O2. In addition, 1 wt% Pt/Ce0.8Zr0.2O2 catalyst showed relatively stable activity with time on stream. The high activity/stability of 1 wt% Pt/Ce0.8Zr0.2O2 catalyst was correlated to its higher Pt dispersion and easier reducibility.