The present invention evaluates the hydrophobicity of a powder. In the present invention, the powder is charged into a mixed solvent composed of a lipophilic solvent and a hydrophilic solvent, the lipophilic solvent is added to the mixed solvent into which the powder has been charged, and the voltage ratio of the mixed solvent is changed at predetermined time intervals. R was measured, a parameter x correlated with the powder concentration was defined for an arbitrary voltage ratio R, and a continuous function HP (x) for the lipophilic solvent ratio corresponding to the x was defined. Then, HP (x) for the required x is used as a hydrophobicity index as a representative value of the lipophilic solvent ratio distribution.本発明は、粉体の疎水性を評価するものである。 本発明では、親油性溶媒と親水性溶媒とからなる混合溶媒に粉体を投入し、粉体が投入された混合溶媒に親油性溶媒を添加すると共に、所定時間間隔毎に混合溶媒の電圧率Ｒを測定し、任意の電圧率Ｒに対して粉体濃度と相関するパラメータｘを定義し、そのｘに対応する親油性溶媒比率についての連続関数ＨＰ（ｘ）を定義した。そして、所用のｘについてのＨＰ（ｘ）を親油性溶媒比率分布の代表値として疎水性の指標とする。
