This study has been carried out to develop a new texturizing process for synthetic filament yarns by solvent - the Solvent-Texturizing. Nylon 6 filament yarn was treated with aqueous solution of formic acid. The creation of crimp was confirmed and the tensile properties and dyeability of treated yarns were examined. The possibility of the Solvent-Texturizing was confirmed. The shape and dimension of crimps were not uniform. The creation mechanism of crimp was confirmed through SEM photographs: The crimps were created by uneveness of width swelling and longitudinal shrinkage in a same cross-sectional area of a filament by the solvent. The crimp ratio was increased with treatment time and formic acid concentration. Especially, the increase of crimp ratio with treatment time was produced mostly by treatment for 1 sec. Remarkable shrinkage, small weight loss, consequent decrease of tensile strength retention, increase of elongation, and dye adsorption were produced by the Solvent-Texturizing under the conditions being used. Most of their changing tendencies were similar to that of the crimp ratio.