A lignin derivative that is extracted from biomass and is used for rubber reinforcement or for use in a molding material is provided. Such a lignin derivative has a number average molecular weight of 300 to 2,000, and contains a component that is soluble in a polar organic solvent, in an amount of 80% by mass or more. When such a lignin derivative is incorporated, a lignin resin composition, a rubber composition, or a molding material, all of which have excellent low hysteresis loss characteristics, elastic modulus, or tensile properties, can be obtained. Furthermore, when a component that is thermofusible is used as the soluble component, a lignin resin composition, a rubber composition, or a molding material, all of which have superior aforementioned characteristics, can be obtained.