This study has been carried out to investigate Electrostatic Precipitator`s(ESP) performance enhancement and removal efficiency of fine particle according to (NH_4)_2SO_4 injection rate. The following conclusions are derived from the these test results : 1)For plant condition cases, according to the variation of concentration agent [(NH_4)_2SO_4] - 10ppm, 20ppm, 30ppm, 40ppm - ESP`s collection efficiency was increased to 97.74%, 98.95%, 99.04%, 99.47%, when inlet dust loading was 2g/㎥. And when inlet dust loading was 3g/㎥, that was increased to 98.19%, 99.16%, 99.23%, 99.58%. 2)It is seen from this experiments that the increasing 30ppm concentration of (NH_4)_2SO_4 increase the collection efficiency and fine particle emission control.