This study measured dyeing properties under different dyeing conditions and levels of antimicrobial activity when man-made fibers are dyed with gallnut, including rayon, tencel, tencel blended fabric, soybean fiber, and nylon non-mordanted. The dye up-take (K/S), color (L*a*b*), and color differences (△E) were measured with a colorimeter, and the number of bacteria present in the dyed fabrics were determined using Staphylococcus aureus and Klebsiella pneumonia as strains. The results are as follows: First, the optimal dyeing conditions for man-made fibers dyed with gallnut are 60 minutes of dyeing time and a 80℃ dyeing temperature. Second, gallnut dye is most effective on soybean fiber and then, in descending order of effectiveness, on nylon, rayon, tencel, and tencel blended fabric. This means that dyeing properties of nitrogen containing fibers are excellent when using gallnut. Third, all man-made fibers are dyed brown with gallnut. This implies dyeing possibility of man-made fibers about gallnut dye, so development and supply of natural dyed goods of man-made fibers can be increased. Fourth, in all man-made fibers dyed with gallnut extract, both Staphylococcus aureus and Klebsiella pneumonia show 99.9% reduction ratios of fungistasis, which indicate antimicrobial activity. Therefore, safe, functional, man-made materials can be developed to relieve symptoms from and treat patients with skin ailments.