Marine diesel engines produce exhaust gas including a lot of SO2 and NOx. This paper proposes a process that is capable of removing NOx and SO2 simultaneously; this process utilizes ozone oxidation and an alkaline countercurrent packed scrubber. Ozone decomposition, oxidation properties of NOx, and removal efficiency of NOx and SO2 were investigated, and the optimal factors were established. The reaction mechanism and products for simultaneous desulfurization and denitration were deduced. Results show that the ozone decomposition rate depends on exhaust gas temperature and initial concentration of ozone. Oxidation efficiency of NOx decreases as temperature rose and initial concentration of ozone reduced. The presence of SO2 has little influence on NO conversion process. CO(NH)(2) is the best reducing additive to reduce the consumption of ozone. The optimal factors for SO2-reduction and NOx-reduction were achieved, such as temperature of 150 degrees C, stoichiometric ratio between ozone and NO of 0.6, and pH about of 8 by alkaline absorption. With this method, about 93% NOx and close to 100% SO2 can be removed at same time and regulations of the international maritime organization (IMO) can be met.