This paper presents the results of an experimental study for a method of increasing the efficiency of electrostatic precipitators for the collection of fly ash particles of submicron size. An alternating electric field was used to induce agglomeration of bipolarly charged particles (bipolar AC-agglomeration). A bench-scale AC-agglomeration test apparatus with bipolar corona charger was constructed. Test aerosol was generated from vegetable oil. The total mass loading was 0.2 gm−3 (5 × 106 particles cm−3), mass median diameter was 0.5 μm. Count median diameter was 0.2 μm, and geometrical standard deviation was 1.8. Residence time in the agglomerator was 4.8 s and the agglomerator field was 5.0 kV cm−1 (rms). Systematic experiments were conducted to investigate the agglomeration efficiency of the system. The percentage decrease in number concentration of 0.1–1.0 μm sized particles was found to be between 17 and 19%.