Compared with commercial alumina Al2O3-c, alumina nanofibers Al2O3-f can improve the activity and selectivity of the impregnated catalysts due to its better cobalt crystallite distribution. Although enhanced cobalt dispersion was observed in alumina nanofiber supported catalyst, a homogeneous Co particle size distribution was difficult to obtain by the conventional incipient wetness impregnation method. Here, we demonstrate an efficiency method to prepare cobalt catalyst supported on gamma-Al2O3 nanofibers with controllable crystallite size distribution. The prepared alumina nanofibers and Co3O4 nanoparticles was mixed and 'rearranged' successfully by an ultrasonication assisted mixing method. The obtained Co-p/Al2O3-f catalyst possesses nearly mono-dispersed cobalt nanoparticles, improved reducibility and interconnected porous structure. Accordingly, more active Co-0 sites are generated, and the catalytic activity and C5+ selectivity are markedly improved; the enhanced stability of the catalyst is due to the inhibited mobility of the cobalt crystals over the alumina nanofibers. (C) 2016 Elsevier Ltd. All rights reserved.