In this paper was examined the influence of mordant usage in dyeing of knitted fabrics with plant extracts, with or without plasma pretreatment, on its degree of coloration. Three different fabrics were used (100% cotton, 100% bamboo and 50% cotton/50% bamboo) with same constructional characteristics and roughly with the same surface mass. Knitted fabrics were treated with aqueous plant extract of Achillea millefolium L., by using bath exhaustion method, and with or without 3% KNaC4H4O6 · 4H2O. The degree of coloration of differently treated knitted fabrics was evaluated with CIELAB method and with stereomicroscope. Antimicrobial properties of knitted fabrics with plant extract of Achillea millefolium L. were tested on Escherichia coli, Staphylococcus aureus and Candida albicans by using parallel streaking method (AATCC TM 147). It was found that the dyeing of knitted fabrics with aqueous extract of the plant Achillea millefolium L. with addition of KNaC4H4O6 · 4H2O caused an incensement of the color fastness after washing compared to knitted fabric dyed without addition of KNaC4H4O6 · 4H2O. It was also found that the processing with plant extract had a positive impact on Escherichia coli, bacteria known as resistant, but only for knitted fabrics after washing.