The three-way catalyst promoters (Ce-Zr)O-2, (Pr-Ce-Zr)O-2 and (Pr-Zr)O-2 were prepared by the sol-gel method. The reduction/oxidation behavior of these mixed oxides was compared. It is shown that the formation of (Pr-Zr)O-2 cubic solid solution at high temperature up to 800degreesC makes it more reducible, and that the ternary solid solution that formed in (Pr-Ce-Zr)O-2 mixed oxides plays an important role in the reduction process. The catalytic performance tests reveal that the introduction of a small amount of praseodymium (Ce-Zr)O-2 favors the light-off temperature of C3H6 and NO and the effectiveness for NO conversion at the lean region.