Natural silk, from Bombyx mori solutions were electrospun into nanofibers, with diameters ranged from 60 to 7000 nm. The effects of electrospinning temperature, Solution concentration and electric field on the formation nanofibers were studied. Optical and scanning electron microscope were used to Study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers became flattened with ribbon-like shape with increasing the electrospinning temperature. The nanofiber diameter increases with the increase in the concentration of silk Solution at all electrospinning temperature. With increasing the voltage of electric field 50 degrees C, morphology of the nanofibers changes from ribbon-like structure to Circular cross section. Referring to the literature the probable mechanism responsible for the change of morphology is pointed out. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 226-234, 2009