An indoor air cleaner consisting of a dielectric barrier discharge system and an electrostatic precipitator (ILS1》) was experimentally investigated. The function of the dielectric barrier discharge is to precharge particles by producing nonthermal plasma before indoor air enters ESP, leading to an enhancement in dust collection efficiency. The dependence of particle size distribution on the plasma discharge was examined to understand the mechanism of the particle precharging. The plasma discharge was found to increase the electrical force of the particles, rather than agglomerate them. Coarse particles in the range of 0.5 to 5.0 ㎛ were observed to be easily collected by this indoor air cleaner, and the present study laid emphasis on the removal of fine particles of 0.3 ㎛. The collection efficiency of the fine particles was largely enhanced by the plasma discharge.