Aims: To purify and partially characterize a bacteriocin produced by a Fusobacterium nucleatum strain. Methods and Results: Following protein precipitation the effect of different treatments on a bacteriocin produced by a F. nucleatum strain named P12.2 isolated from a patient with periodontitis was evaluated. The antagonistic activity of the intracellular fraction obtained at 80% ammonium sulphate was preserved at pH values from 6 0 to 9 0 and showed to be sensitive to high temperatures and to treatment with proteases. The fraction was submitted to sequential steps of gel filtration, ion exchange, and reverse phase chromatography, and SDS-PAGE. Data obtained by mass spectrometry revealed that the molecular mass of the protein was 27296 Da. Conclusions: For the first time a bacteriocin produced by a F. nucleatum strain was purified and characterized. Significance and Impact of the Study: This is the first description on characterization of a bacteriocin produced by F. nucleatum. It is possible that the bacteriocin plays a role in the regulation of population levels of periodontopathic organisms.