Cellulose acetate (CA) nanofibers containing Ag ions, CA (as-spun), were fabricated by electrospinning with 0.5 or 1 wt% of silver nitrate (AgNO3). CA nanofibers containing Ag ions/nanoparticles (NPs), CA (UV), were prepared by UV irradiation of as-spun CA nanofibers. Also, cellulose nanofibers with Ag NPs, CA (UV+DA), were prepared by deacetylating the UV-irradiated CA nanofibers. The antimicrobial activities of Ag ions or NPs in nanofibrous matrices were examined against Gram-negative Escherichia colt and Gram-positive Staphylococcus aureus. From conventional antimicrobial test for 18 h, both Ag ions and Ag NPs in the CA or cellulose nanofibers exhibited strong antimicrobial activity against S. aureus. From kinetic antimicrobial test against E. coli for 30 min, the CA (as-spun) showed faster bactericidal activity than the CA (UV) and CA (UV+DA) samples. (C) 2013 Elsevier B.V. All rights reserved.