This study investigated the dyeing properties of silk fabrics with Annatto. The dye stuff was extracted by distilled water at $60^{circ}C$, 10minutes, 1:100 of bath ratio. Dyeability(K/S) and color fastness of silk fabrics were tested under conditions of various concentrations, time, temperature, repeat-numbers of dyeing, pH, mordants variables and methods of mordanting. The highest absorbance was found in methanol extract of Annatto. The optimum dyeing concentration, time and temperature of silk fabrics with Annatto were 25%(o.w.f.), 60min and $60^{circ}C$ respectively. The K/S value showed higher in post-mordanting than in pre-mordanting, and especially post-Fe mordant showed highest K/S value. In the case of colorfastness, Cu-mordanted fabrics were good washing fastness. Dry cleaning fastness appeared 4-5 grades and light fastness showed lowest grade.