A series of polypropylene (PP) nanocomposite fibres containing respectively 0, 0.5, 1, 3, and 5 wt% ZnO nanoparticles (NPs) were prepared by melt spinning. The antimicrobial activity of these fibers against Staphylococcus aureus (ATCC 6538) as a Gram-positive bacterium and Klebsiella pneumoniae (ATCC 4352) as a Gram-negative bacterium was evaluated. It was confirmed by scanning electron microscopy that the dispersion of the NPs within the PP matrix was homogeneous. Although such homogeneity the fibers are unable to exhibit antimicrobial activity. The absorption properties of the fibers was then investigated and found to be inadequate, so cold plasma and chemical finishing were applied to improve their absorptivity. After this treatment the PP/ZnO nanocomposite fibers exhibited increasing antimicrobial effectiveness with filler content. In addition, mechanical and thermal characterization tests showed that increasing concentration of ZnO–NPs improved the mechanical properties of the fiber due to the interface between the matrix and the nanoparticles sharing the stress. The crystallinity of the fibers was found to decrease by about 7% as the level of ZnO increased to 5%. This was attributed to the more rapid cooling experienced in the presence of ZnO particles of high thermal conductivity.