Nanosized Ce0.7Zr0.3Mx oxide particles (M=Zn, Sn, x = 0.1, 0.3, 0.5) with 10-20 nm diameter were synthesized by a coprecipitation method. Their structure and morphology were characterized by XRD, FT-Raman and TEM. Zn did not incorporate well into Ce0.7Zr0.3 oxide, but Sn did. The catalytic performance of these particles for CO oxidation was investigated between 150-400 degrees C under severe conditions. Ce0.7Zr0.3Sn0.5 had the best performance with the lowest light-off temperature range (175-210 degrees C). A temperature hysteresis was observed in all catalysts studied.