Particle charging is an essential process for electrostatic precipitators (ESPs) in removing particles. A particle charge measurement system, which can adjust the flue gas temperature, was designed to study the effects of the flue gas parameters (viz., temperature and humidity), particle composition, and discharge electrodes on particle charging. The particle charge increased with the temperature when the applied electric field strength was constant. For particles with a diameter of 0.73 µm, the average charge increased by 30% (from 140 e to 183 e) when the temperature increased from 300 K to 363 K. Furthermore, with a constant electric field strength of –4.2 kV cm–1, the average charge increased by 98% when the relative dielectric constant increased from 4.5 to 11.8. Increased relative humidity significantly accelerated particle charging. For particles > 0.1 µm, the average charge increased by more than 50% when the relative humidity increased from 30% to 80%. Optimizing the discharge electrode also enhanced charging. After the wire electrode (d = 1 mm) was replaced by a ribbon electrode, particle charging increased by more than 75% for 0.7 µm particles at –4.2 kV cm–1.