Two types of corona-discharge reactors, a deposition-type reactor in which negative ions deposit at the anode and a wetted-wall reactor in which negative ions are absorbed into a liquid film on the anode, are applied to removals of C2F3Cl3. BY the deposition-type reactor, the removal efficiency from Na increases with the decrease of the inlet concentration, suggesting that this reactor can be applied to remove extremely low concentrations of C2F3Cl3. When the C2F3Cl3 concentration is high, there is an optimum concentration of coexisting H2O to give the maximum removal efficiency. When O-2 is mixed, the removal efficiency decreases. The removal mechanism is discussed on the basis of dissociative electron attachment, radical reaction, and particle formation. When the C2F3Cl3 concentration is high, the wetted-wall reactor shows a higher removal efficiency than the deposition-type reactor. On the other hand, when the C2F3Cl3 concentration is low, the result is opposite.