In the fields of sanitation and medicine, there is an urgent need for the development of convenient methods for imparting antibacterial properties to materials. Polypropylene nonwoven fabrics (PP NWFs) are one of the most common polymer materials; however, it is difficult to impart antibacterial properties to PP NWFs due to their low reactivity and complicated structures. In this study, we discovered that oxidation using photo-activated chlorine dioxide radical (ClO2) gas is a useful method for antibacterial modification of PP NWFs, without the need for any antibacterial agents or multi-step treatments. The as-prepared PP NWFs exhibited excellent antibacterial activity against both Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive). Interestingly, the solvent used to wash the product was analyzed to reveal the formation of nanoparticles around 80 nm in diameter during the oxidation step, particularly at 80 C.