This study examines the mordanting effect and multi functional properties of silk fabrics dyed with onion shell extracts that were mordanted with gallnut. The contents of this study are as follows. First, the optimum dyeing conditions were investigated by measuring the K/S value that depended the on dyeing conditions when silk fabrics were dyed with onion shell extracts. Second, the color, brightness, and chroma differences that appear after mordanting with gallnut were investigated by measuring the K/S and Munsell value. Third, the color fastness and antimicrobial activity were measured. When silk fabrics were dyed with onion shell extracts, the optimum dyeing conditions were a dyeing temperature of $70^{circ}C$, a dyeing concentration of 160%, and a dyeing of time 30min. After mordanting with gallnut extracts, the K/S value increased remarkably and was larger in pre-mordanting than post-mordanting. The H value displayed yellow-red in all cases of pre and post mordanting. However, the H value was more reddish in the order of non-mordanting<post-mordanting<pre- mordanting. The mordanting of gallnut extracts did not influence the V value. The C value decreased by the mordanting of gallnut extracts and was smaller in post-mordanting than pre-mordanting. In the case of post mordanting (300%), wet cleaning fastness showed a 4-5 grade, dry cleaning fastness showed 5 grade, perspiration fastness showed 4~4-5 grade, and lighting fastness showed 4-5 grade. All of the dyeing fastness were improved by mordanting and dyeing fastness of post-mordanting was superior to that of pre-mordanting. There was no antimicrobial activity in the case of onion shell extracts, but the antimicrobial activity of gallnut extracts was excellent. The silk fabrics dyed with onion shell extracts did not show an antimicrobial activity, but the silk fabrics dyed with onion shell extracts and mordanted with gallnut extracts showed antimicrobial activity of 99.9%.