The purpose of this study is to investigate surface color change and effects of mordants on the K/S values of silk and wool fabrics dyed with Lac extract, according to the mordanting methods and conditions such as temperature, concentration and time of the mordanting bath. The results were as follow; 1 K/S values of the silk and wool fabrics according to the temperature of the mordanting bath were shown a slight decline beyond 40$^{circ}C$. 2. Surface color of the silk changed from red to reddish purple and that of the wool showed red tone when mordanted with Aluminum postassium sulfate, Copper acetate and Copper (II) sulfate regardless of the mordanting conditions. 3. The light and dry cleaning fastness of silk and wool fabrics dyed with Lac extract according to the mordanting methods were very good.