In previous studies (1–3), it was found that two kinds of lipoproteins, termed α- and ß-lipovitellin, exist in egg yolk, and the isolations of these lipoproteins and their contents in yolk proteins were reported. Both of them represented a single peak in buffer of pH 9.8, but further informations on their homogeneities were reserved for the following study. This paper deals with more detailed studies upon the homogeneities and some properties of α- and ß-lipovitellin. In the pH range from 4.9 to 10.5, ß-lipovitellin has shown a single peak on electrophoresis and an isoelectric point at pH 5.9. Ultracentrifugation at pH 9.8 has represented the heterogeneity of both lipoproteins. The variation of the mobility of ß-lipovitellin produced by a change in the buffer composition at constant ionic strength has reflected differences in the binding of the various buffer ions to the protein. The influences of pH and ionic strength on the solubility of ß-lipovitellin have been studied.