Engine technologies using efficient combustion and down-sizing turbo have become important in order to reduce automotive CO2 emissions. However, the exhaust gas temperature also becomes lower by these technologies. As a result, the catalyst performance becomes lower. Therefore it is necessary to develop low temperature active catalysts to reduce emissions. This research was focused on Pd/CeO2, and it’s able to oxidize CO at low temperatures.In order to increase the catalyst activity, the addition of some elements to the CeO2 was studied. Zn addition was found to have an advantage to reduce the CO light off temperature by 60 °C. Then, we tried to clarify the cause of improvement. As a result, it made clear that the Zn addition promotes the active oxygen release from the CeO2 surface.However, repeated engine exhaust gas tests indicated a decline in purification performance. The carbonate inhibited the active oxygen release from the CeO2, resulting in declining the catalyst purification performance. To improve the performance of catalyst, Ba was added which has a strongly CO2-absorption element because of high basicity. This modified Ba/Zn/CeO2 showed no decline in purification performance even after the repeated engine test.Next the effect of Ba/Zn/CeO2 addition into conventional catalyst was evaluated by vehicle emissions in LA4 cycle test. As a result, emission was improved by about 10% as compared to no addition. The newly developed material, Ba/Zn/CeO2 has been employed in mass-production catalysts for the 2016 model year.