As the SO3 emissions from coal-fired flue gas have received increasing concerns, experiments on the removal characteristics of sulfuric acid aerosols in the wet electrostatic precipitator (WESP) system were carried out by using a pilot plant. The physical properties of sulfuric acid aerosols before the WESP system were analyzed as also the removal performance in the WESP system. Moreover, the effects of operating parameters on the removal and the effect of sulfuric acid aerosols on PM2.5 removal were discussed. The results displayed that plenty of submicron sulfuric acid aerosols exited before the WESP system, and the majority ones were smaller than 0.1 mu m. The corresponding removal efficiencies were mainly from 30 to 65%, and the fractional removal efficiency had a distinct decline for aerosols with sizes from 0.1 to 1 mu m. Furthermore, with the increase of the operating voltage and the decline of the inlet gas temperature and the inlet concentration of sulfuric acid aerosols, the removal effect was promoted. Besides, the existence of sulfuric acid aerosols was beneficial for the PM2.5 removal in the WESP system, especially for submicron ones. The tendency was more obvious when the inlet concentration was increased.