The graft polymerization of acrylic acid (AA) on PA6 yarn was examined. Prior to the grafting process, the fibers were activated with a benzene solution of benzoyl peroxide. The effects of the main process parameters and auxiliary additives on the degree of grafting, quantity of the homopolymer formed during grafting, effectiveness of grafting, extent of conversion, and grafting ratio were determined. The resultant fibers, containing carboxylic groups in their structure, were additionatly modified with penicillin, neomycin, or gentamycin to obtain antibacterial fibers in relation to Gram-positive and Gram-negative microorganisms (Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa). This was confirmed in vitro by measuring the stunted growth zones of the above-mentioned bacteria. The modified fibers show different activities in relation to the microorganisms, being dependent on the type and quantity of the added biocide. The kinetics of antibiotic release into water was examined and described by means of a mathematical equation. The release of antibiotics into solution proceeds for quite a long time after which there is still enough antibiotic on the fibers to provide them with antibacterial properties.