For the purpose of application to new natural dyestuff, the dyeability of Purple onion shell extract was analyzed. It was dyed in cotton fabric according to various dye weight, dyeing temperature, dyeing time. And the effects of mordanting conditions were examined as color differences and color fastnesses. The dyeaffinities were increased as were increased dye weight, especially 100% owf. The optimum dyeing condition of Purple onion shell extract was 40minutes at $60^{circ}C$. The dyeaffinity was increased at pre-mordanted condition, and color difference was increased distinctly at post mordanted condition. The hue of all mordanted cotton fabrics changed into Yellow where as non mordanted cotton fabric was Red. The color fastnesses of mordanted cotton fabrics were generally not so god, but light fastness was improved in post-Cu mordanted fabric.