Blending selected polymer materials in the membrane fabrication process has been widely investigated for dense film membrane in order to improve the membrane gas separation performance. However, such a strategy has not been fully explored on hollow fiber membrane, which is preferred in industry for gas separation. In this study, Matrimid (R) 5218 hollow fibers with 0-12 wt% additive (PEG or PEO-PDMS copolymer) were fabricated via phase inversion technique. The effects of additives on the hollow fiber's gas transport properties were discussed in terms of the membrane morphology and surface composition, gas separation performance as well as plasticization and aging property. Both additives showed significant impact on the membrane structure, particularly influencing the skin layer of the hollow fiber. However, the copolymer also displayed surface aggregation behavior which resulted in the modification of skin layer composition. The increase in the concentration of PEG improved the CO2 permeance from 21 GPU (without PEG) to 37 GPU (with 12 wt% PEG) and the hollow fibers with 12 wt% PEO-PDMS copolymer displayed a doubled CO2/N-2 selectivity compared to the fibers without the additive. Addition of PEG reduced the CO2 plasticization pressure while PEO-PDMS improved the plasticization resistance of hollow fibers. (C) 2014 Elsevier B.V. All rights reserved.