Antibacterial and antifungal peptides found in houseflies (Musca domestica) in large number are indispensable components of its immune defense mechanism. In this study the anterior tip of the larvae of housefly was cut off with a pair of fine scissors and hemolymph was collected and exuded in an ice-cold test tube. From the hemolymph an antifungal substance was isolated by solid-phase extraction combined with reverse phase-high performance liquid chromotography (RP-HPLC) and named as Musca domestica antifungal peptide-1 (MAF-1). Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed its molecular weight was 17 kDa. UV absorption spectra revealed that this antifungal substance possessed the characteristics of protein peptides. Analysis by fingerprint-identification and tandem mass spectrometry suggested MAF-1 was an unknown protein. Edman degradation identified the sequence of 30 amino acids of its N-terminal which matched no peptide in the MASCOT search database, indicating MAF-1 was a novel insect antifungal peptide. Mass spectrometry showed the precise molecular weight of MAF-1 was 17203.384 Da. Its isoelectric point was acidic.