Nylon-4,6 nanofibres with diameters ranging from about 1 mu m down to 1 nm were prepared by electrospinning. The fibre diameter was varied by adjusting the concentration of the polymer solution. Electrospinning of a concentrated solution of as high as 20% nylon-4,6 by weight in formic acid produced a ribbon-like electrospun fibre with a ribbon width of about 850 nm. A semi-dilute concentration of 2% nylon-4,6 by weight produced the thinnest nylon-4,6 nanofibres with diameters of 1.6 nm or less. A small amount of pyridine was added to the electrospinning solution to avoid the formation of beaded nanofibres in the course of electrospinning at low concentrations. Scanning and transmission electron microscopy were used to characterize the size of the nanofibres. An ultra-thin nylon-4,6 nanofibre of 1.2 nm diameter might contain six or seven nylon-4,6 molecules in a typical cross-section of the fibre.