Antibacterial peptides function as effectors for defense in innate immunity. In mammals, they are implicated in the barrier protection of epithelia where their expression can be induced during infection and inflammation. Over a dozen of antibacterial peptides have been identified in humans. Among these, defensins and cathelicidins have been well characterized. Two types of defensins (alpha- and beta-defensins) are recognized based on the presence of their conserved six cysteine residues, whereas cathelicidins are characterized by a homologous cathelin sequence in the pro-region and a variable antibacterial C-terminal sequence. Human beta-defensins and cathelicidin hCAP18/LL-37 are mainly expressed in epithelial tissues where mast cells are present. Here we review the structure of human beta-defensins and cathelicidin, and describe their multiple activities on mast cells to induce chemotaxis, degranulation and prostaglandin D(2) production, acting through receptors coupled to G-protein-phospholipase C pathway. Thus, in addition to their bactericidal activities, epithelial cell-derived antibacterial peptides may modulate the inflammatory responses by recruiting mast cells to inflammation foci and inducing the degranulation as well as prostaglandin production from this cell population.