A novel positive-polarity electrostatic precipitator (ESP) was developed using an ionization stage (0.4 × 0.4 × 0.14 m3) with 16 carbon fiber ionizers in each channel and a collection stage (0.4 × 0.4 × 0.21 m3) with parallel metallic plates. The single-pass collection efficiency and clean air delivery rate (CADR) were measured by standard tests using KCl particles in 0.25–0.35 μm. Performance was determined using the Deutsch equation and established diffusion and field charging theories and also compared with the commercialized HEPA filter-type air cleaner. Experimental results showed that the single-pass collection efficiency of the ESP ranged from 50 to 95% and decreased with the flow rate (10–20 m3/min), but increased with the voltage applied to the ionizers (6 to 8 kV) and collection plates (−5 to −7 kV). The ESP with 18 m3/min achieved a CADR of 12.1 m3/min with a voltage of 8 kV applied to the ionization stage and with a voltage of −6 kV applied to the collection stage. The concentration of ozone in the test chamber (30.4 m3), a maximum value of 5.4 ppb over 12 h of continuous operation, was much lower than the current indoor regulation (50 ppb).