Nylon-6,6 nanofibers were electrospun at an elongation rate of the order of 1000 s(-1) and a cross-sectional area reduction of the order of 0.33 x 10(5). The influence of these process peculiarities on the intrinsic structure and mechanical properties of the electrospun nanofibers is studied in the present work. Individual electrospun nanofibers with an average diameter of 550 nm were collected at take-up velocities of 5 and 20 m/s and subsequently tested to assess their overall stress-strain characteristics; the testing included an evaluation of Young's modulus and the nanofibers' mechanical strength. The results for the as-spun nanofibers were compared to the stress-strain characteristics of the melt-extruded microfibers, which underwent postprocessing. For the nanofibers that were collected at 5 m/s the average elongation-at-break was 66%, the mechanical strength was 110 MPa, and Young's modulus was 453 MPa, for take-up velocity of 20 m/s-61%, 150 and 950 MPa, respectively. The nanofibers displayed a-crystalline phase (with triclinic cell structure). (c) 2006 Wiley Periodicals, Inc.