Abstract: A series of complex oxide La1-xCexCoO3 catalysts were synthesized at low temperature through a combustion process, in which x is among 0, 0.1, 0.2, 0.4 and 0.6 corresponding to the quantity of La3+ partial substitution by Ce4+. And the catalysts were characterized for phase composition using chemical analysis and xray diffraction. The surface characterization of the catalysts was determined by SEM. The catalytic activity of the catalysts in removal of NOx, THC and particulate matter (PM) from diesel exhaust gases were examined in details using temperatureprogrammed reaction (TPR) technique. The results show that after partial substitution of La3+ with Ce4+ the oxygen vacancy concentration increases significantly and Co3＋-Co2＋ system is formed , and consequently the catalytic activity in removal of THC and NOx is significantly improved. But for PM, the effect is not so obvious, and the possible catalytic mechanism was also presented. The doped catalysts also show good stability.