In this work, shape manipulation in porous CeO2 nanofibers was successfully achieved by a simple electrospinning technology with high quality and high reproducibility. By simply tuning the electric field strength during electrospinning, the diameter of as-spun nanofibers composed of Ce(acac)(3) and polyvinylpyrrolidone can be precisely controlled. As a result, the morphology of nanofibers can change from columnar to celery-like and belt-like structure. The formation mechanism of this intriguing diameter-dependent morphology can be assigned to the gradient evaporation of solvent across the nanofiber. After calcination at 500 degrees C, porous CeO2 nanofibers were obtained, showing unusually observed celery-like or belt-like morphologies. These intriguing CeO2 nanofibers exhibited good thermal stability in terms of phase structures and morphologies up to 700 degrees C. The fibrous CeO2 mats were active toward soot combustion with decreased activation energy, compared with commercial samples. Among three kinds of shapes, the fibrous CeO2 mats made of columnar-like nanofibers were endowed with the lowest activation energy of 120.1 kJ/mol, due to the most effective contact between soot and CeO2 surface, regardless a loose contact mode.