The body-surface of an animal is important spot for rejection of infectious microorganisms. Exoskeleton, skin, scale and mucus are the most elementary participants of self-defense mechanisms. Antimicrobial factors existing/induced near the bodysurface are effective in killing microorganisms and preventing severe infectious disease. The sea hare, Dolabella auricularia is a marine shell-less gastropod from which four cytotoxic proteins dolabellanins A, C, P and E, were previously found. These dolabellanins are glycoproteins, with molecular weights higher than other invertebrate self-defense factors: tachypresins, insect defensins secropins and sarcotoxins. We recently isolated another type of cytotoxic factor, dolabellanins B1, B2 and B3 from the skin and body surface area of sea hares. Among the three new factors, dolabellanin B2 and B3 are the small molecules which showed antimicrobial activity. In this meeting, we discussed the antifungal and antibacterial activity and the structure of dolabellanin B2 and dolabellanin B3.