Ultrafine fibers of a laboratory-synthesized new biodegradable poly(p-dioxanone-co-(L)-lactide)-block-poly(ethylene glycol) copolymer were electrospun from solution and collected as a nonwoven mat. The structure and morphology of the electrospun membrane were investigated by scanning electron microscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and a mercury porosimeter. Solutions of the copolymer, ranging in the lactide fraction from 60 to 80 mol % in copolymer composition, were readily electrospun at room temperature from solutions up to 20 wt % in methylene chloride. We demonstrate the ability to control the fiber diameter of the copolymer as a function of solution concentration with dimethylformamide as a cosolvent. DSC and WAXD results showed the relatively poor crystallinity of the electrospun copolymer fiber. Electrospun copolymer membrane was applied for the hydrolytic degradation in phosphate buffer solution (pH = 7.5) at 37 degreesC. Preliminary results of the hydrolytic degradation demonstrated the degradation rate of the electrospun membrane was slower than that of the corresponding copolymers of cast film. (C) 2003 Wiley Periodicals, Inc.