In previous works, it was elucidated that baicalein and baicalin belonging to flavonoids can be mutually separated by solvent extraction with trialkylphosphine oxides. In this work, in order to obtain the basic information of separation of various kinds of flavonoids, i.e., flavone, flavonol, 7,8-dihydroxyflavone, baicalein and baicalin, their aqueous solubilities and the extraction behavior with various kinds of extractants in hexane were examined. From these results, a separation process of flavonoids is proposed in the case that baicalin is a target substance.