Ultrafine porous cellulose triacetate (CTA) fibers were prepared by electrospinning with methylene chloride (MC) and a mixed solvent of MC/ethanol (EtOH) and their intra- and inter-fiber pore structures was investigated. Ultrafine porous CTA fibers electrospun with MC had isolated circular shape pores with a narrow size distribution in the range of 50-100 nm. In the case of ultrafine CTA fibers electrospun with MC/EtOH (90/10 v/v), they had interconnected. larger pores in the range of 200-500 nm. These porous structures were induced by phase separation resulting from the rapid evaporation of solvent during the electrospirming process. However, non-porous corrugated fibers were obtained from MC/EtOH (85/15 v/v) and MC/EtOH (80/20 v/v) due to their lower vapor pressure. The pore sizes in ultrafine CTA fibers electrospun with MC showed a bimodal distribution centered at similar to 17 and similar to 64 nm. CTA fibers electrospun with MC/EtOH (90/10 v/v) showed the greatest porosity due to their larger intra-fiber pores and fiber diameter. (C) 2005 Elsevier.B.V All rights reserved.