Defensins are abundant and widely distributed peptides in human and animal tissues that are involved in host defence. Defensins not only have the ability to strengthen the innate immune system but can also enhance the adaptive immune system by chemotaxis of monocytes, T-lymphocytes, dendritic cells and mast cells to the infection site. Defensins also improves the capacity of macrophage phagocytosis. A greater understanding of how these peptides act in the healthy, gingivitis and periodontitis conditions would definitely open new opportunities for identification, prevention and treatment of periodontal diseases. This discussion focuses on recent studies about biological function of defensins in human diseases and animal models.