This work presents the results of the first‐principals study of magneto‐optical properties of oxidized Co nanowires on vicinal Pt surfaces. Two types of vicinal platinum surface (Pt(332) and Pt(322)) are studied to analyze the effect of surface structure on oxidation process and on the magneto‐optical properties of oxidized Co nanowires. The study reveals the change of magnetic coupling in Co nanowire under oxidation, which is sensitive to step edge geometry of vicinal surface. The dielectric tensor and reflectivity are calculated for oxide structures in order to find their main features in optical characteristic. Besides, the reflectance difference spectra are constructed for pure and oxidized nanowires in order to reveal the effect of interplay between magnetic state and oxidation on the optical properties of magnetic nanowires, which can be useful for tailoring their magnetic properties in spintronic devices.