Seven new peptaibols, atroviridins A-C composed of 20 residue amino acids and neoatroviridins A-D with 18 residues, were isolated from the culture broth of fungal strain F80317. The strain F80317 was identified as Trichoderma atroviride from its morphological and cultural characteristics. These compounds showed antimicrobial activity against Gram-positive bacteria and phytopathogenic fungi, and exhibited significant cytotoxicity to human cancer cell lines in vitro. Atroviridins showed significant membrane-perturbing activity responsible to their antibiotic action.