Antimicrobial polypropylene (PP) fibers were produced using polyhedral oligomeric silsesquioxanes (POSS) nanoparticles during melt spinning process. Octa ammonium POSS (QA-POSS) was used in three different concentrations of 0.5, 1 and 3 wt% for the modification of PP fiber. Antimicrobial efficiency of QA-POSS and modified PP fibers were examined against four different pathogenic bacteria, namely Escherichia coli, Bacillus cereous, Staphylococcus aureus and Proteus vulgaris. Tensile, thermal and morphological properties of fiber samples were also characterized by tensile testing, differential scanning calorimeter (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), respectively. According to test results, modified PP fibers showed antimicrobial effect against selected four different bacteria. The antimicrobial effect of modified PP fibers increased as the added amount of QA-POSS increased regardless of bacteria types. The modified fiber samples exhibited the best antimicrobial effect against Bacillus cereous with a bacterial reduction of 97 %.