The collection efficiency of many electrostatic precipitators (ESPs) must be improved in order to fulfill the particulate emission standard, which has become increasingly rigorous. According to classical collection theory, decreasing the gas velocity for an electric field is one of the most effective methods of enhancing the collection efficiency. Thus, we proposed a side-flow ESP, which, compared to its conventional counterpart, requires a far lower gas velocity for the electric field when the gas flow rate is constant. First, using aerodynamics, a theoretical expression of the collection efficiency and dust re-entrainment lift force was derived for a turbulent flow. The calculations indicated that a greater increase in efficiency was achieved by decreasing the gas velocity, which potentially reduces dust re-entrainment, than by lengthening the electric field. To confirm the advantages of the side-flow ESP, the collection efficiency and dust re-entrainment were measured in comparison experiments with a conventional ESP, in which talc powder with a medium diameter of 11.6 µm was used as the test dust. The dust concentration at the inlet averaged ~1400 mg m–3, and the strength of the electric field ranged approximately from 3 to 4 kV cm–1. The experimental results indicated that the emitted concentration and the dust re-entrainment were 45% and 42% lower, respectively, for the side-flow ESP than for the conventional ESP at the same gas flow rate.