The catalytic activity of several cerium/zirconium mixed oxides for TWC applications has been investigated with the aim of optimising the Ce/Zr composition. Their catalytic activity was surprisingly high, considering that no noble metal was present in the composition, particularly for oxidation reactions (CO and C3H6), while their reduction activity was very small (NO). The specific activity of the mixed oxides for CO and C3H6 was found to be the contribution of the individual specific activity of the single oxides. The best activity in practice (lowest T-0 and T-50 and highest X-773) was found for the mixed oxide with a Ce/Zr ratio of 80/20, as a combination of its high specific activity and the highest specific surface area.