Nanostructured titanium dioxide (TiO₂) electrodes, prepared by anodization of titanium, are employed to probe the electron-transfer process of cytochrome b₅ (cyt b₅) by surface-enhanced resonance Raman (SERR) spectroscopy. Concomitant with the increased nanoscopic surface roughness of TiO₂, achieved by raising the anodization voltage from 10 to 20 V, the enhancement factor increases from 2.4 to 8.6, which is rationalized by calculations of the electric field enhancement. Cyt b ₅ is immobilized on TiO₂ under preservation of its native structure but it displays a non-ideal redox behavior due to the limited conductivity of the electrode material. The electron-transfer efficiency which depends on the crystalline phase of TiO₂ has to be improved by appropriate doping for applications in bioelectrochemistry. Nanostructured TiO₂ electrodes are employed to probe the electron-transfer process of cytochrome b₅ by surface-enhanced resonance Raman spectroscopy. Concomitant with the increased nanoscopic surface roughness of TiO₂, the enhancement factor increases, which can be attributed to the electric field enhancement.