Rutile TiO layers were formed on substrates of Ti–(0–10)at%Au alloys by a simple process of air oxidation, and their antibacterial activities were evaluated under visible-light irradiation (λ ≥ 400 nm). Au was introduced into the TiO layers on Ti–(1–10)at%Au alloys and existed as both metallic Au nanoparticles and dissolved Au ions. The TiO layers that formed on Ti–5at%Au and Ti–10at%Au alloys exhibited visible-light photocatalytic activity, that is, degradation of stearic acid and antibacterial activity against Escherichia coli. These visible-light activities were attributed to the surface plasmon resonance of metallic Au nanoparticles and the decrease in bandgap energy caused by dissolved Au ions. The formation of hydroxyl radicals observed under visible-light irradiation is attributable to antibacterial activity. From a cost perspective, a Ti–5at%Au alloy is more suitable as a substrate for the formation of a TiO layer with antibacterial properties than a Ti–10at%Au alloy. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 991–1000, 2019. 2 2 2 2 3+ 3+