Recently, phenolic resin has been a promising precursor to synthesize electrospun carbon ultrafine fibers with well-controlled pore structure favorable for CO2 capture. We report the facile and large-scale preparation of freestanding microporous carbon ultrafine fibers from resole-type phenolic resin by electrospinning and following one-step carbonization, and investigate for the first time their CO2 adsorption performance at ambient temperature. The obtained samples were characterized by scanning electron microscopy, Raman spectra, X-ray photoelectron spectroscopy and N-2 adsorption. Small average diameter of 820 nm, high specific surface area (650 m(2) g(-1)) and narrow micropore size distribution are associated with the prepared fibers. Remarkably, the ultrafine fibers possess much more ultra-small micropores (0.50-0.63 nm) than common polyacrylonitrile-based activated carbon nanofibers and commercial porous carbon samples. With such well-designed structure, the resultant fibers show outstanding CO2 equilibrium adsorption capacities and good reversibility. At 25 degrees C, the stable capture capacity of the fiber is 2.92 mmol g(-1) at 1 bar and 0.44 mmol g(-1) at 40 mbar, which offers great potentials for CO2 capture and storage. (C) 2015 Elsevier B.V. All rights reserved.