Microporous fibers can potentially increase diffusional properties of three-dimensional nonwoven scaffolds used for tissue engineering applications. We have investigated the use of a water-dispersible copolyester, sulfonated copolyester (SP), to create micropores in composite fibers containing a blend of SP and poly(lactic acid) (PLA) at 1, 3, 5, and 10% SP content. PLA and SP were blended at 175 C in a microcompounder followed by extrusion of composite fibers and removal of SP from composite fibers by using hydrodispersion to form micropores in the composite fibers. Differential scanning calorimetric studies on unhydrolysed composite fibers showed that SP was partially miscible M PLA. Fourier transform infrared mapping of composite fiber cross sections revealed that SP was randomly dispersed throughout the cross section where the degree of dispersion depended on the SP content. As revealed by the scanning electron micrographs, the size of the micropores was dependent on the SP content. Micropores on fiber cross sections were observed in fibers above 3% SP indicating that at least 3% SP content is needed to produce droplet morphology of SP in these fibers. These results show that SP can be successfully used in a blend with PLA to produce microporous fibers to fabricate three-dimensional nonwoven scaffolds for tissue engineering applications. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3350-3361, 2010