The effects of we treatments on the stregth, birefringence and viscosities of cold-drawn nylon-6 were studied. The results were as follows; 1. Wet heat treatment changes tensile properties; it lowers the force to elongate yarns up to 20%. The higher the treating temperature, the lower the force needed to elongate the yarn. 2. Chemical change does not occur. 3. Wet heat treatment makes the birefringence to increase. The higher the concentration of a dye the more increase of birefringence appears, but it does not improve yarn quality.