Two block copolymers consisting of biodegradable segments of poly(ethylene glycol) (PEG) and poly(P-caprolactone) (PCL) with slight different lengths of soft hydrophilic segments (PEG) and molecular weight were produced. The copolymer with shorter PEG segments and higher molecular weight was named copolymer A, while the other copolymer B. Both copolymers were dissolved in dichloromethane at the same concentration (5% w/v) and electrospun. Different combinations of spinning voltage (SV) and distance needle to collector were used. Electrospun A copolymer showed curly and uniform fibers with an average diameter of 2 mu m, while B copolymer fibers were straight, uneven, and much thinner (sub-micrometric). In the latter case, fiber bundles and beads were also present. Viscosity measurements on the solutions before spinning showed a viscosity of 13.0 mPa s for A copolymer solution and 5.5 mPa s for B copolymer. The mechanical properties on dog-bone shaped samples from the electrospun material evidenced that A copolymer had much higher stress and elongation at break but approximately the same elastic modulus as compared to B copolymer. Fiber morphology and mechanical properties of electrospun block copolymers are deeply influenced by different amount and length of soft and hard segments, and block copolymers can be the best suited systems to fit several applications because of the broad range of properties they Show upon changing the composition ratio and molecular weight of components. (C) 2008 Wiley Periodicals, Inc.