Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (similar to2.3 mum) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10-15 wt %, and more ultrafine CA fibers (0.46 mum) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5-11, 2004.