In China, particles in flue gasses emitted by coal-fired power plants are mainly cleaned using electrostatic precipitators (ESPs). However, some power plants have experienced decrease in the collection efficiency of ESPs after burning low-sulfur and high-alumina coals. In order to make ESPs collect effectively the PM2.5 in the flue gas before and after SO3-flue gas conditioning (FGC), the resistivity, size distribution, chemical composition, and specific surface of the fly ash sampled from Tuoketuo Power Plant ESPs were analyzed using the portable dust electrical resistivity test instrument, Bahco centrifuge, constant law, and the COULTERTM SA 3100TM specific surface area analyzer. Simultaneously, the SO2 emission was monitored by a continuous emission monitoring system. The results showed that, when the SO3 content increased by 34.3 mg/m(3) (12 x 10(-6) volume fraction), the resistivity of the fly ash in the flue gas decreased by approximately two orders of magnitude. In addition, the surface tension of the fly ash diminished, the adhesive force and size increased, and the specific surface area decreased. The efficiency of the ESPs increased from 96.7% to 99.8%. The SO2 emisSions and the content of SO3 in the fly ash have not changed appreciably before and after SO3-FGC. Therefore, SO3-FGC is an effective method of improving the efficiency of ESPs in collecting high-alumina coal fly ash. (C) 2013 Elsevier B.V. All rights reserved.