Loess was selected as one of the natural dyes and dye solution was extracted from it. With the dyes extracted from loess, the sample fabrics were dyed at 10, 20, and 30 minutes and then $CuSO_4$ was used to treat the dyed fabrics on the concentration of 3%, and 5%. Color difference and colorfastness of the sample fabrics with dyeing time and concentration of post-mordanted agent were analysed. The results were as follows: 1. Effective dying time was 20 minutes since any more dye up-take to the fabrics did not occur after that time. 2. There was distinctive dyeing effect according to whether post-mordanted method was done or not, but there was little effect between post-mordanted concentration of 3% and 5%. 3. There was no effect of the colorfastness on the post-mordanted concentration. The abrasion and laundering colorfastness of post-mordanted fabric samples was better than those of no post-mordanted fabric samples and the light colorfastness of the fabric samples was good regardless of post-mordanted method.