The influence of O-2 concentration on the decomposition of halide gases (CCl4, CHF3, CHClF2) by non-thermal plasma was investigated using a wire-in-tube type reactor. Results showed that the decomposition ratio of CCl4, CHF3 and CHClF2 in the plasma reactor was lower in O-2-N-2 atmosphere than in N-2 atmosphere. The major reaction products detected from the decomposition of CHClF2 in O-2-N-2 atmosphere were HCl, Cl-2, HF, F-2, CCl2F2, COCl2, COF2 and CO2. In the case of non-thermal plasma decomposition with in-situ absorption of Ca(OH)(2), the decomposition ratio of CHClF2 was increased, and halogen byproducts were scavenged by Ca(OH)(2), independent of reaction atmosphere. With an increase in O-2 concentration, the fraction of CO2 produced by the plasma decomposition of CHClF2 was increased in both the reactors with and without Ca(OH)(2) absorbent.