Purified rat ceruloplasmin is extraordinarily unstable in storage at −70 °C. In a 20 mM phosphate buffer, pH 7.0, the ferroxidase and amine oxidase of ceruloplasmin are over 90% inactivated within two weeks. Holoceruloplasmin stored for three months in a 20 mM barbital buffer (or acetate buffer), pH 7.0 (or pH 5.5) was transformed into an apo-protein and amine (o-dianisidine) oxidase of ceruloplasmin was inactivated by 50–55%. The patterns of ferroxidase activity loss were similar to those of amine oxidase activity loss. On the contrary, when holoceruloplasmin was mixed with rat serum albumin, transformation into apoceruloplasmin was significantly prevented in a 20 mM barbital buffer, pH 7.0 (or 20 mM acetate buffer, pH 5.5). Consequently, ferroxidase and amine oxidase activities of ceruloplasmin were not inactivated and the immunochemical reactivity was not changed. These results can be applied for laboratorial and clinical purposes.