Narrowly diameter-distributed single-walled carbon nanotubes (SWCNTs) were purely achieved by a facile technique combining microwave irradiation with mixed acid-assisted dispersion. Using this process, besides removal of conventional impurities, both small SWCNTs with highly chemical reactivity and the outer layers of large double-walled carbon nanotubes with more topological defects were preferentially eliminated, retaining only pure SWCNTs of which the diameter distribution was significantly narrowed. The chemical structure of resulting materials was carried by Raman spectroscopy, and electron microscopies. Results revealed that the technique employed is of great efficacy not only for purifying carbon nanotubes, but also especially for narrowing carbon nanotubes. The dual effects of purifying and diameter distribution narrowing make this method promising for achieving high purity single-walled CNTs of specific types. The purification mechanism of the present technique was discussed in detail. (C) 2012 Elsevier B.V. All rights reserved.