Various formulations of soy protein isolate (SPI), poly(ethylene oxide) (PEO), and Triton X-100 (p-tertiary-octylphenoxy polyethyl alcohol) were evaluated for their effects on the electrospinning behavior and morphology of SPI nanofibers. In aqueous solution, SPI that was denatured using a combined thermal and alkaline treatment could not be spun into fiber. However, when similar to 0.8% (wt/wt) PEO was added, SPI could be spun into fiber readily by grounding spinneret and applying positive electrode to the collector plate, resulting in fibers of 200 to 260 nm in diameter. PEO acted synergistically with SPI in enhancing the electrospinning of the protein solution through increasing the solution viscosity and reducing the electrical conductivity. Furthermore, SPI of various morphologies (fibers, "beads/fibers," beads) can be achieved by varying SPI and PEO concentrations. Over the range of concentrations explored, the surfactant added did not affect significantly the surface tension of the fiber-forming solution. Nevertheless, the surfactant did improve the electrospinning behavior of SPI by facilitating the dispersion of SPI powder for forming homogeneous polymer solutions. Electrospinning of SPI obtained from different commercial sources also resulted in significant variation in fiber morphology.