Dielectric barrier discharge (DBD) and catalysis hybrid process was used to remove nitrogen oxides and particulate matters from diesel engine exhaust. The DBD reactor converts a part of NO into NO2, and then the exhaust gas containing the mixture of NO and NO2 enters the catalytic reactor where both NO and NO2 are reduced to N-2. The effect of energy density (power input divided by gas flow rate) and reaction temperature on the removal of nitrogen oxides was investigated with a stationary diesel engine. The hybrid process was able to remove about 80% of the initial nitrogen oxides at an energy density of 25 J/L and 150 degrees C. The removal of particulate matters did not largely depend on the electrode structure, but it was a strong function of the energy density. On the basis of 80% removal efficiency, the energy yield for nitrogen oxides was 40 eV/molecule while that for particulate matters was 83 kJ/mg. The present study suggests that this kind of hybrid process can be applied to simultaneous removal of nitrogen oxides and particulate matters from diesel engine exhausts.