The vitellin of the red flour beetled Tribolium castaneum Herbst was purified and characterized. The vitellin of T. castaneum was purified by the FPLC techniques, anion exchange chromatography and gel permeation chromatography. In native-polyacrylamide gel electrophoresis, vitellin of T. castaneum was detected as a single band. This native vitellin has molecular weight of 440 kDa. The vitellin of T. castaneum is composed of three polypeptides, designated Vnl (178 kDa), Vn2 (168 kDa) and Vn3 (52 kDa) in SDS-polyacrylamide gel electrophoresis. Three subunits of vitellin were presented in the female adult hemolymph and egg extracts, but not observed in the male. These three polypeptides gradually decreased during embryogenesis. Polyclonal antiserum raised against purified vitellin reacted with the three polypeptides, Vnl, Vn2 and Vn3. Antisera raised against Vn1 and Vn2 cross-reacted with the two large subunits, Vnl and Vn2, respectively. Another subunits Vn3, however, was not cross-reacted with these two antisera. Also, antiserum raised against Vn3 did not cross-react with the Vn1 and Vn2.