The polypropylene/silver nanocomposite fibers were prepared for the attainment of permanent antibacterial activity to common synthetic textile. The fibers were melt-spun by co-extrusion of polypropylene (PP) and PP/Ag master-batches using general conjugate spinning. Master-batches were made up of mixture of PP chips and nano-sized silver powder. The antibacterial efficacy of spun fibers was excellent not when the master-batch used as the core, but when used as the sheath. The antibacterial activity of nano-silver in fibers was evaluated after certain contact time and calculated by percent reduction of two kinds of bacteria; Staphylococus aureus and Klebsiela pneumoniae. For the characterization, differential scanning calorimetry (DSC) and wide-angle X-ray diffractometer (WAXD) were used for analysis of structure, thermal and crystallization behavior of the spun-fibers. Scanning electron microscopy (SEM) was carried out to observe particle distribution on the nanocomposite fibers. (C) 2003 Kluwer Academic Publishers.