A very basic secreted protein which displays antifungal activity was isolated from the medium of the mold Aspergillus giganteus. The protein consists of 51 amino acid residues whose sequence was determined as Ala-Thr-Tyr-Asn-Gly-Lys-Cys-Tyr-Lys-Lys-Asp-Asn- Ile-Cys-Lys-Tyr-Lys-Ala-Gln-Ser-Gly-Lys-Thr-Ala-Ile-Cys-Lys-Cys-Tyr-Val- Lys- Lys-Cys-Pro-Arg-Asp-Gly-Ala-Lys-Cys-Glu-Phe-Asp-Ser-Tyr-Lys-Gly-Lys-Cys- Tyr-Cys . Disulfide bonds were formed between Cys7-Cys33, Cys14-Cys40, Cys26-Cys28 and Cys49-Cys51. These results suggest that the antifungal protein forms a loop structure and is similar to phospholipase A2.