The submicron fibers were prepared via electrospinning the styrene-isoprene-styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N-dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8-15 wt %; the morphology, diameter, structure, and mechanical performance of as-spun fibers from PS and STS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1580-1586, 2009