Here, cobalt-doped plasma electrolytic oxidation (PEO) coatings with different cobalt contents were prepared on Ti implants. The cobalt ions in the PEO coating exhibited a slow and sustainable release and thus showed excellent biocompatibility and enhanced cell adhesion. In vitro enzyme-linked immunosorbent assay and real-time polymerase chain reaction assays demonstrated that the cobalt-loaded Ti showed immunomodulatory functions to macrophages and upregulated the expression of anti-inflammatory (M1 type) genes and downregulated expression levels of pro-inflammatory (M2 type) genes compared with that of pure Ti sample. High cobalt content induced increased macrophage polarization into the M2 type. Furthermore, the findings from the in vivo air pouch model suggested that cobalt-loaded Ti could mitigate inflammatory reactions. The present work provides a novel strategy to exploit the immunomodulatory functions of implant materials.