Nano-sized beads and non-woven porous fiber constructs of poly(epsilon-caprolactone) were produced by electrospinning. Nearly spherical beads with diameters between 900 nm and 5 mum were produced with dilute solutions with less than 3 wt% PCL. In this case, the initial jet of solution may split into many mini jets almost at the end of the needle and each minijet gradually disintegrates into small droplets. Beyond a critical solution concentration of about 4 wt% PCL, the jet may undergo extensional flow, splitting and splaying to produce a web of interconnected fibers with mean diameters on the order of 300 to 900 nm. Intermolecular entanglements play a dominant role in stabilizing the fibrous structure. A uniform fibrous structure was obtained at 40 kV while at 20 kV a large fraction of beads were present in the electrospun polymer. The fiber diameter in the PCL deposited on the collector typically exhibits a bimodal distribution. Electrospinning lowers the degree of crystallinity in the polymer. (C) 2004 Kluwer Academic Publishers.