Until date, CSαβ-type (ASABF) and α-helical-type (nematode cecropin) antimicrobial peptides have been isolated from nematodes. In addition, some genes encoding putative antimicrobial peptides have been reported. Nematode antimicrobial peptides are noteworthy from two general aspects. First, these peptides are important components in the immunity of the nematode, Caenorhabditis elegans, which is widely used as a model of innate immunity and host-pathogen interaction. Second, as few samples have been isolated from lower-invertebrates, these peptides are key in revealing the evolution of antimicrobial peptides. In this review, we describe the features of nematode antimicrobial peptides and their contribution to immunology and molecular evolution.