Mastoparans are a family of small peptides identified from the venom of hymenopteroid insects. Although they have been characterized as early as 1979, and so far are recognized as a leading biomolecule in potential drug therapy, their precursors, mastoparanogen, have still not been determined. In this paper, several mastoparans from the venom of the wasp Vespa magnifica (Smith) are reported. The cDNA of mastoparanogen is 236 base pairs in length, and encodes 40 amino acid residues, including a N-terminal acidic fragment and a C-terminal mature basic mastoparan, which contain multiple acidic amino acid residues and a tetradecapeptide with three lysines, INLKAIAALAKKLLG, respectively. The glycine at the tetradecapeptide end is the donator of -NH(4) for the amidation of the leucine at the C-terminal. As far as we know, this is the first report of the precursor of animal mastoparan.