The pore dimensions and distribution of carbon membranes can be finely adjusted by various post-treatment methods to meet different separation needs and objectives. In this study, the post-oxidation effect on the gas permeation performance was investigated in the poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) derived carbon membranes with oxidation conditions (oxidation temperature and time). The post-oxidized carbon membranes were prepared by carbonization at 700 degrees C, followed by the air-oxidation. The permeances of gas species increased with increasing oxidation temperature and time due to increase in pore characteristic properties, such as pore volume, pore size and its distribution. The influence of the post-oxidation on the extent of the gas permeance modification was higher for gas species having a large molecular size. The carbon membranes post-oxidized at a low temperature (e.g., 200 degrees C) and a short time (e.g., 1 h) showed high permeation performance. The post-oxidation on the permeation results clearly showed that the gas permeation properties could be modified by appropriate oxidation conditions. (C) 2007 Elsevier B.V. All rights reserved.