Abstract: A method for preparing fibers having antimicrobial properties which involves melting a melt-extrudable thermoplastic composition and extruding the molten composition through multiple orifices to form streams of molten composition which are cooled to form fibers. The thermoplastic composition includes a thermoplastic polyolefin and an additive. The additive is an antimicrobial siloxane quaternary ammonium salt which can be either of two general classes: (1) a trisiloxane having a pendent quaternary ammonium group and a molecular weight of from about 600 to about 1,700; and (2) an ABA-type siloxane having a polydispersity of up to about 3.0 and a weight-average molecular weight of from about 800 to about 2,000, in which a central siloxane moiety is terminated at each end by a quaternary ammonium salt group. The anion in general can be any anion which does not adversely affect the thermal stability of the salt.