The effect of the solvent on the formation of high aspect ratio ultrafine fibers in polyamide-6 using an electrospinning technique was examined systematically. In this study, formic acid, dichloromethane, acetic acid, chlorophenol, hexafluoroisopropanol, and trifluoroacetic acid via single and mixed solvent system were used for the production of high aspect ratio nanofibers in polyamide-6. Formic acid and mixtures of formic acid/dichloromethane, formic acid/acetic acid, and formic acid/chlorophenol can lead to the very clear dissolution of polyamide-6, enabling their subsequent electrospinning to obtain high aspect ratio nanofibers. Formic acid was found to be the most suitable solvent system for obtaining high aspect ratio nanofibers in polyamide-6. The conductivity of polyamide-6 in formic acid was very high demonstrating an increasing level of free ions in solution. The average diameter of the high aspect ratio nanofibers was approximately one order of magnitude lower than that of main fibers. These findings suggest that the formation of high aspect ratio nanofibers relies strongly on the specific properties, such as the poly-electrolytic behavior of polyamide-6 in the solvent.