This study is carried out to examine the effects of simultaneous dyeing and antimicrobial finishing of wool yarns. Wool yarns were dyed with acid dye along with colloidal silver nanoparticles through the exhaustion method in a one-bath. Different concentrations of nanosilver were examined to evaluate its influences on the color and the antibacterial properties of the yarns. The antibacterial property of the sample has been tested by a Gram-negative bacterium Escherichia coli and a Gram-positive bacterium Staphylococcus aureus. Also, the tenacity of wool yarns, color, and rubbing fastness of the dyed yarns has been measured. The color fastness against washing and antibacterial property of the dyed yarns after 10 laundering cycles was also considered. The fiber morphology was studied by SEM pattern, EDX, and X-ray diffractometer. The results showed that the wool yarns dyed with acid dye along with 25 ppm of silver nanoparticles exhibited a very good antimicrobial effect even after 10 laundering cycles on S. aureus while the rubbing fastness remained unchanged, and the color fastness and tenacity were even improved. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1405-1411, 2011