Human defensins, found in the blood, intestinal tract and epithelial cells, are small, cystin-fich cationic peptides with special structure. They have broad-spectrum antimierohial activities involving Gram-positive, Gram-negative, epiphyte and enveloped virus, and they are crucial part of innate immune mechanism, by certain close relationship with some inflammatory diseases. This article reviews the biochemical properties, distribution in human body, biological roles and relationship with some diseases connected to them.