This study was conducted to determine the serum vitellogenin (VTG) concentration changes during the ovulation period in elkhorn sculpin, Alcichthys alcicornis. The results of sepacryl S-300 showed that the molecular weight of VTG could be 380,000. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) analysis may indicate that the purified VTG consists of three subunits with molecular weights of 180,000, 118,000 and 85,000, respectively. Yolk protein purified from the egg extracts was eluted on an equilibrated sephacryl S-300 column, and its molecular weight was estimated 250,000. The precipitation lines of the female serum against the antiserum of the egg extracts were fused completely by immunoelectrophoresis and immunodiffusion analysis. VTG was detected in the serum, and hepatocytes from males injected with $17eta-estradiol;(E_2).$ Furthermore, VTG was immunochemically similar to yolk proteins. The concentration of VTG was high before ovulation $(9.80pm0.81-11.02pm0.09 mg/ml),$ and then decreased rapidly after ovulation $(less;than;6.19pm0.59 mg/ml).$ This study suggested that VTG was synthesized in the liver by the action of $E_2$ and released to blood, and then incorporated into oocytes.