Enzyme mimics have been developed as a new generation of antibiotics with broad-spectrum antibacterial properties to combat bacteria. In this study, a peroxidase mimic was constructed from nanodiamonds (NDs) to treat periodontal pathogen-induced infections with decreasing damage of periodontal tissues by traditional drug therapy. The oxygenated nanodiamonds (O-NDs) have excellent enzymatic activity over a broad pH range, and locally activated free-radical generations from low concentration of hydrogen peroxide, presenting a significantly enhancement in bacterial cell membrane disruptions and breaking down biofilms. In the presence of trace non-toxic hydrogen peroxide, topical rinse treatments with O-NDs restrain the development of bacterial infection in vivo, thus preventing and ameliorating the course of periodontal inflammation in a rodent model. More importantly, the enzymatic activity of O-NDs can accelerate the wound healing around sites of periodontal infection in time. The platform of nanodiamond-based enzyme mimic is built having high performance antibiotic-free periodontal antibacterial therapy, and can be extended to other fields of medical applications.