We have isolated ferritin from the blood of the marine bivalve mollusc Scapharca broughtonii in which blood iron levels were high (approx. 4,000∼5,000 ㎍Fe/100 ml). The blood ferritin had a M_r of ca. 500,000 with a single subunit type having a M_r of ca. 21,000. The isolated ferritin contained 1,400∼2,000 atoms Fe/molecule on average. The bivalve ferritin core was examined preliminarily using an electron microscope and its electron diffraction pattern implied characteristic lines of ferrihydrite. The preliminary Mo¨ssbauer spectra of the S broughtonii ferritin showed a striking difference. T_(ord) was estimated ca. 20 K and T_B was lower than 13 K. Ferroxidase activity of the bivalve apoferritin was assayed and characterized. Apoferritin catalyzes the oxidation of Fe(II) to Fe(III). The initial rate of Fe(II) oxidation was dependent on Fe(II) concentration and a linear dependence of initial rate on protein concentration was observed.