The structure of gonadotropic hormone of an invertebrate (Asterina pectinifera) was elucidated. The gonadotropic hormone is a peptide with molecular weight 4500 to 4900 composed of two subunits, wherein the structure of the protein has the structure bound by SS bridges formed between SH residues of cysteines contained in the subunits. Mixing and oxidizing these two subunits after their synthesis enables to give a peptide (gonadotropic hormone) with gonad-stimulating activity.