The preparation of acrylonitrile, methylacrylate, and 2-acrylamido-2-methylpropanesulfonic acid terpolymer fiber and its dyeing by anionic dyes were examined. The stability of the dye in modified polyacrylonitrile fiber was studied. It was shown that the modified fiber had bactericidal properties. The fiber physicomechanical properties changed insignificantly as a result of the modification and coloring.Acrylonitrile terpolymer fibers (trademark nitron) account for a quarter of the volume of chemical fibers manufactured in the Republic of Belarus. They make up about 65% of the staple fibers used by the textile industry. The operational characteristics (high physicomechanical properties, light-and water-resistance, etc.) of these fibers are highly promising for further rapid development of this type of fibrous raw material.Moreover, polyacrylonitrile (PAN) fibers used in wool blends for producing textiles have several advantages and a drawback associated with the poor dyeing by anionic dyes (chrome, acid, direct) that are usually used to color wool items. Therefore, PAN fibers are dyed before being blended with wool during production of blended items in order to ensure even coloring of the finished product. This complicates significantly the industrial process.Another problem that is just as important and must be solved during production of wool blends designed for general use (in hotels, trains, medical establishments, military barracks, etc.) where the danger of infection by pathogenic microorganisms arises is how to give them bactericidal properties. On one hand, this enables the risk of spreading the infection to be reduced; on the other, it protects the natural fibers from biodegradation.Thus, the development of the production technology for PAN fibers with both bactericidal properties and the ability to be dyed by dyes traditionally used to color wool is important and critical. Successful resolution of several industrial and health problems related to the development and production of such fibrous materials would allow the variety of items based on PAN fibers to be expanded.An analysis of the primary structure of PAN fibers produced on an industrial scale from the terpolymer of acrylonitrile (AN) (a = 90.4 mass%), methylacrylate (MA) (b = 8.2 mass%), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) (c = 1.4 mass%) showed that the functional groups capable of producing PAN fiber colored stably by anionic dyes were missing:Bactericidal properties can be imparted to fiber by treating it with quaternary ammonium salts. Modifiers can be absorbed by PAN gel-fiber in several ways: -penetration into the polymer through a system of connected pores; -occurrence of sorption-desorption processes on the internal gel-fiber surfaces; -formation of ionic bonds between polymer acidic groups and cationic modifiers.