An object of the present invention is to provide a technique for separation/collection of a lignin derivative which is useful for the separation of a lignin derivative having a 1, 1-diphenylpropane unit and/or a unit derived from the 1, 1-diphenylpropane unit from a mixture system containing the lignin derivative. In the Present invention, a lignin derivative having a 1, 1-diphenylpropane unit and/or a unit derived from the 1, 1-dipheylpropane unit is allowed to contact with a metal oxide in a liquid medium, thereby separating the lignin derivative in the form retained on the metal oxide.